Facepalm

Almost all of the comments below this are incorrect in assuming how lever handles operate.

In cheaper or lower grade lever handles, both handles operate together and operate the latch. When it's locked, the lever stays rigid and does not move. It is very easy to stand with your own bodyweight on the lever and break it, therefore getting in.

Only in higher grade lever handles do both handles operate independently while also not engaging the latch, preventing the handle from staying rigid and less likely of being broken.

So assuming this is a shitty or lower grade lever handle, getting locked into your apt this way is 100% plausible.