Some supporting context to Peckish's answer, with primary sources.

CNN has the full transcript of the speech. Here is the context around the relevant section in full, I've added bold highlighting to some particularly relevant parts:

...This is a vital position to our counterterrorism efforts. Nobody suggests Mr. Szubin is not qualified; he's highly qualified. Unfortunately, his nomination has been languishing up on the Hill. And we need the Senate to confirm him as soon as possible.

 

Meanwhile, we continue to ramp up our training and support of local forces that are fighting ISIL on the ground. As I've said before, this aspect of our strategy was moving too slowly, but the fall of Ramadi has galvanized the Iraqi government. So with the additional steps I ordered last month, we're speeding up training of ISIL forces, including volunteers from Sunni tribes in Anbar province.

 

More Sunni volunteers are coming forward; some are already being trained and they can be a new force against ISIL. We continue to accelerate the delivery of critical equipment, including antitank weapons to Iraqi security forces, including the Peshmerga and tribal fighters. And I made it clear to my team that we will do more to train and equip the moderate opposition in Syria.

 

Now all this said, our strategy recognizes that no amount of military force will end the terror that is ISIL unless it's matched by a broader effort, political and economic, that addresses the underlying conditions that have allowed ISIL to gain traction. They have filled a void and we have to make sure that, as we push them out, that void is filled.

 

So as Iraqi cities and towns are liberated from ISIL, we're working with Iraq and the United Nations to help communities rebuild the security, services and governance that they need and we continue to support the efforts of Prime Minister Abadi to forge an inclusive and effective Iraqi government that unites all the people of Iraq, Shia, Sunni, Kurds and all minority communities. [continues]

The speech is very, very consistently about training and supporting the opposition to ISIS / Daesh / ISIL / IS, with details about who exactly is being trained and what the plan is for them.

If "training of ISIL forces" was intentional, they'd be training ISIL to be "a new force against ISIL", "fighting ISIL on the ground" to "end the terror that is ISIL" and ensure that "Iraqi cities and towns are liberated from ISIL".

It's a very embarrassing slip of the tongue, but it's clear from the context that this is what it is.

Some supporting context to Peckish's answer, with primary sources.

CNN has the full transcript of the speech. Here is the context around the relevant section in full, I've added bold highlighting to some particularly relevant parts:

...This is a vital position to our counterterrorism efforts. Nobody suggests Mr. Szubin is not qualified; he's highly qualified. Unfortunately, his nomination has been languishing up on the Hill. And we need the Senate to confirm him as soon as possible.

Meanwhile, we continue to ramp up our training and support of local forces that are fighting ISIL on the ground. As I've said before, this aspect of our strategy was moving too slowly, but the fall of Ramadi has galvanized the Iraqi government. So with the additional steps I ordered last month, we're speeding up training of ISIL forces, including volunteers from Sunni tribes in Anbar province.

More Sunni volunteers are coming forward; some are already being trained and they can be a new force against ISIL. We continue to accelerate the delivery of critical equipment, including antitank weapons to Iraqi security forces, including the Peshmerga and tribal fighters. And I made it clear to my team that we will do more to train and equip the moderate opposition in Syria.

Now all this said, our strategy recognizes that no amount of military force will end the terror that is ISIL unless it's matched by a broader effort, political and economic, that addresses the underlying conditions that have allowed ISIL to gain traction. They have filled a void and we have to make sure that, as we push them out, that void is filled.

So as Iraqi cities and towns are liberated from ISIL, we're working with Iraq and the United Nations to help communities rebuild the security, services and governance that they need and we continue to support the efforts of Prime Minister Abadi to forge an inclusive and effective Iraqi government that unites all the people of Iraq, Shia, Sunni, Kurds and all minority communities. [continues]

The speech is very, very consistently about training and supporting the opposition to ISIS / Daesh / ISIL / IS, with details about who exactly is being trained and what the plan is for them.

If "training of ISIL forces" was intentional, they'd be training ISIL to be "a new force against ISIL", "fighting ISIL on the ground" to "end the terror that is ISIL" and ensure that "Iraqi cities and towns are liberated from ISIL".

It's a very embarrassing slip of the tongue, but it's clear from the context that this is what it is.