"Unit" and "Integration" (and E2E) are the most bullshit "technical" terms we have to deal with on a regular basis as an industry. At best, they can only tell you that integration tests are on average more liberal in their use of system calls than unit tests, that is if the codebase in question even has both.

While this dev you encountered might have had no idea what they were doing, a most charitable explanation is that they may subscribe to the idea that the "unit" is a business usecase within a single service (often a 1:1 correspondence with an endpoint, but sometimes even more than one, e.g. a form upload with a separate signed upload step to a 3rd party service).

FWIW the concept of small/medium/large as presented in the Google testing blog is a much more useful denomination.