Windows has a facility to log a user in before they enter passwords and effectively when you log in you are simply "unlocking" your account. This is done to ensure that updates are performed upon boot and keeps your system up to date.
It could be this facilitythat you are seeing and the shop simply powered it on to test that whatever they did to repair it worked. They could have then tried it again a few days later to see that it had not lost a significant amount of charge or was still able to charge.
Unless you can see signs that all your data has been accessed or other programs installed it does not necessarily mean that they were doing anything unexpected or nefarious.
You can find out more about that setting and how to disable it at Windows 10 - Users already logged in at boot