It depends on what is confirmed first and who sets up the F2F trade. If you didn't agree to, and or confirm a f2f trade yet, you can still match for the basic trade listing. If you had agreed to the f2f trade before matching on a basic trade, your basic trade would have been put on hold so you don't match with anyone.
I'm going to guess that the user you did the f2f trade with, set the trade up? If so, he could have chosen a game you had listed in your collection. Even while matched in a basic trade, another user can set up a f2f trade for that game with you. When you try to accept the f2f trade though, you will get the error message informing you that this game is already in a basic trade.
To boil it down, you can still get a F2F request from a user while matched in a basic trade. You just wouldn't be able to accept it if also matched with another user in the basic trade listing.
I hope that answers your questions.