Let us suppose, to simplify the numbers, that all these passes are on designed rollouts where the pass is thrown nearly at the line of scrimmage.
1st down: QB throws an incomplete pass that travels 25 yards in the air.
2nd down: QB throws an intermediate sideline completion for 11 yards that the receiver catches as he runs out of bounds.
3rd down: QB throws a screen pass for 3 yards that the receiver takes for a total of 29 yards.
total air yards: 39
air yards per attempt (average depth of target): 13.0
total passing yards: 40
yards per attempt: 13.33
The receiver was not (necessarily) tackled right when he caught the ball.
I don't understand what the problem is supposed to be with the cited stats. Let's not beat around the bush, here: is the claim being made that "air yards per attempt" correlates to
good QBs? I'm pretty sure I can find more stats on (say) Mahomes' air yards per attempt, but I'm not going to bother if we can't even agree on what that stat is supposed to tell us.
P.S. Just to address an earlier statement:
Air yards per attempt literally cannot be higher than yards per attempt.
This was a mistake by me. Air yards per
completion cannot be higher than yards per attempt, but we aren't measuring air yards per completion.