The thing on the top of the trigger is the loader, just like FAMAS, the loader and the ejector is separated for accessibility. Push the loader, the ejector will load some rounds.
@ J192: Exactly, that's why it's normal for the *casing ejector* to be at the back of the rifle, which seems to be, but the thing above trigger also looks like a *casing ejector*, that's what confuses me. And what I want to say at last is that if the *casing ejector* is above the trigger is pretty much, false. I know it's a small detail, but not like others I do care about them.
@ Yates: That's what I fear of... there are two possibilities, there is something similar above the magazine, which would rather be what you mean. If the *casing hole* is above the trigger though, it's weird, how do the casings reach there ?