Except we're talking about a game here and its completely irrelevant what tank crew would or would not see.
That is correct, it is a gameplay element. The tank can see the infantry the infantry can see the tank both can and do shoot at each other but the infantry does 0 damage to the tank. Which leads to my question why was the choice made to make the infantry shoot at the tank in the first place when they do 0 damage. It has no other gameplay function other than alerting the other player of the presence of the infantry.
edit: And not even that if I think about it, the tank would turn its turret and fire at them and then the player would notice it, too. Seconds later maybe when they wouldn't have opened fire in the first place. Of course you can lure the tank with an infantry squad but they don't have to shoot to do that. A sniper for example will get himself killed.
A new player will yell at the screen in disbelieve why his sniper thought it was a good idea to shoot at the Panzer to give away his position because he is not yet familiar with the hold fire mechanic.