There’s no indication that (that I can find) at Halfaya Pass Rommel’s guns only had AA rounds. HE or possibly dedicated AT rounds maybe have been available.
Even the AA rounds could be set for point detonation, making them function essentially the same as HE rounds designed for hitting structures. While not designed for penetration like dedicated AT rounds, in WW2 88mm HE is an absolutely massive payload for direct fire against a tank.
Rommel was going up against Matilda II tanks which had been designed to survive against 37mm and maybe 50mm anti-tank guns. 88mm absolutely cored out a lot of tanks.
Isn’t/wasn’t the anti aircraft ammunition of a FlaK essentially different from anti tank ammunition although the calibre is/was nominally the same?
Yes, but: