when the flag falls, its usually over, with very few exceptions (one being, the opponent did not pay attention, then someone wins, and THEN they look at the clock..)
draw by position requires a position where no one CAN win. Here, white and black can both queen a pawn if the other side makes a mistake. No draw.
Chess tournament rules are available online so you can go read them. You won't find anything about a4.
Here is an endgame, in G/3 time variant, you just claimed the win when you opponents flag/or his time ran out, he says it is a theoretical draw, but he has 2 pawns and his king and I have a pawn and a king. I thought, when someone'stime ran out you lose, but he says he claimed the draw, no matter what, what chess rule book doe he reads?
Position after flag fell/or time ran out: there was no DRAW offer before the game started or even before his time ran out.