"It is the first direct conflict within Israel's boundaries since the 1948 Arab–Israeli War."
The statement is certainly technically incorrect. But with some qualifications one can discern what is meant here.
Israel boundaries
Firstly, some countries and organizations do not recognize Israel's existence at all, in which case speaking of boundaries/borders is simply meaningless. As far as the organizations and states recognizing Israel are concerned, its territory is very different from that designated by the United Nations Partition Plan for Palestine of 1947, which triggered the declaration of Israel as an independent state and the first recognition by other states.
What is mostly meant by the Israeli boundaries in western media (to which we can assign Wikipedia in English) is its borders before the Six Day War, which is really the 1949 armistice lines, often referred to as the Green Line or 1967 borders. This excludes some of the territories that are considered parts of Israel under the Israeli law - notably the Golan heights, the eastern parts of Jerusalem, and parts of what is known as the West Bank.
Scale of incursions within the Green line since 1949
Starting from the armistice of 1949 (which is mistakenly put in 1948 in the quoted Wikipedia sentence) Israel fought wars mostly outside of the Green line. Six Day War was initiated by Israel (at least technically), and resulted in Israel capturing more territory. The War of Attrition and Yom Kippur War were fought largely in the territory outside of the Green Line that Israel controlled at that time - notably in the Golan Heights (with Syria) and Sinai Peninsula (with Egypt.)
Incursions within the area delimited by the Green line by various Palestinian and Lebanese groups did take place, just to give a few examples:
However, none of these raids resulted in a number of casualties and the scale of fighting comparable to the one that took place on 7 October 2023. Indeed, the number of the casualties on the Israeli side in the 2006 Lebanon War was 121 of military personnel and 46 civilians (including two non-Israeli citizens.) This is a significant number for a country with population of about 8 million (e.g., if scaling to the size of the US and comparing to 9/11 or the American casualties in Iraq or Afghanistan.) In other words, from the Israeli perspective, the fighting is more resembling a full-scale war than a terrorist raid, and it is the first time that the fighting on this scale took place within the Green line. This is the best that I can offer as the interpretation of the Wikipedia claim.
As an extra information, similar unexpected losses in 2006 Lebanon War and in Yom Kippur War resulted in creation of State Commissions of Inquiry (Winograd Commission and Agranat Commission respectively) whose conclusions had far-reaching political consequences.