Sources with direct knowledge tell TMZ, TMC certainly was part of the local Phi Theta Kappa chapter at the Community College of Allegheny County -- but just on paper, because in terms of anyone knowing or interacting with him ... we're told that simply never happened.

We're told Thomas never attended any events or functions within the honor society as far as PTK brass is aware -- and more importantly ... we're told no one even knew this guy's name/face until it was reported in the media that he was a member of the org.

The only thing we're told Phi Theta Kappa honchos knew about Thomas is that he paid his one-time fee to join ... a measly $95. Beyond that ... our sources say nobody knew a thing about the dude.

We're told some within the organization theorize he simply joined on a superficial level to pad his resume in an effort to help him get to better schools after the fact -- which jibes with the fact that we know he got into two major universities ... and was set to attend one in the fall.

While we knew he was a member of PTK, we checked their social pages just yesterday, and couldn't find any pics featuring Thomas ... now, it seems clear that's because there aren't any.

In other words, we're told nobody at PTK can speak to Thomas' character or habits -- the only thing anyone knows about him at this point is that he tried to kill Donald Trump.

As we all know ... Thomas fired multiple shots off during a 26-second span last Saturday, clipping Trump in the ear and killing a volunteer fire chief before snipers returned fire and took him down.

Trump recounted his whole harrowing tale Thursday night at the Republican National Convention ... saying he thinks God watched over him and helped save his life.