It is long know that Facebook allows you on purpose to log in with the password case reversed or the first character capitalized (see this article). They do this while storing only a hashed password. Are you seeing that more differences are allowed?
Apparently, they also have some similar usability features for the email address. Automatically "correcting" gmail.comm to gmail.com is actually harmless, since there's (currently) no comm tld, so nobody would actually have a valid gmail.comm email address. I am however surprised that they would allow gmadil.com (currently for sale) or a different username, as that could be someone else's email address.
They might have decided that usability is of utter importance and, if there is a log in attempt for an email address for which there is not an account, automatically attempt the log in with the most similar username, but -while not completely bad- it doesn't seem a good approach, as someone else could sign up tomorrow with the [email protected] email and, although unlikely, also use Password123 as password, then what?
Update: This had been tested a few years back by Lukas on Does correcting misspelled usernames create a security risk? and apparently logging in with a misspelled email address only works when you have not deleted Facebook cookies from your earlier session. Thus, it only autocorrects your email address when it knows that you used to log in as [email protected], and otherwise fails.
Note: Another user had suggested earlier that the cookies could be playing a part of this, but it is now in a deleted answer.