I initially thought it was for a red card too. Then, I pulled out my phone, fired up AppleTV and saw what they were really reviewing. I said "Oh man, if they call this a penalty, people are going to lose their fucking minds." Apologies to my 8-YO.
I also saw the push in the back live (I sit right on the side of that penalty area). I was worried it would be whistled live, but then never imagined it would be sent for review.
Fans can't help but keep score, and when one team (1) is given a red, (2) sees an opponent offsides reversed in favor of a goal, and (3) called for a penalty in the box after review, it does not even matter if the calls were right. Those fans will feel hard done. In contrast, whenever I read or hear sports officials discuss make-up calls, they always scoff a the idea. They don't just say it's wrong, or never done, you can tell they have absolute contempt even for the suggestion. They have goldfish memory and just wants to get the next call right. And I think they're right to do so.
But, "correct" does not mean objectively the right call if you had an omniscient official with perfect lines of sight and judgment. "Correct" after review means was the original call was clearly and obviously wrong with the replays we have.
The offside was borderline. But I've seen too many poor angle offside videos that seemed obvious turn out to be wrong after the perfect angle is shown. We had one just a few games ago, though I can't remember the specifics. Unless he was shown something we did not see, I don't think we had a reliable angle.
Meanwhile the PK push was a judgment call. Nothing about the original call was wrong. It legitimately could have gone either way. People like to say that if you take too much time it's not clear and obvious, but that's only sometimes true depending on the nature of the call. If you reverse based on objective fact, such as whether the defender got ball or not, or it can take a bit to find the right camera and for your mind to pick out the sequence and elements and see through a tangle of bodies. But judgment calls are different. If you look at a judgment type replay and don't immediately go, wow, that's a lot worse or less egregious than I thought, it will never become clear and obvious no matter how many times you look at it. There arguably is not even an objective right or wrong answer.
Best justification for the ref's handling was he did not see the push at all, so the video showed him a fact he missed, but he obviously struggled with the sufficiency judgment call aspect.
The most consistent and frustrating problem with VAR is inconsistent application of the standard. Maybe that was objectively a PK, and maybe not. It doesn't matter. He misapplied the standard while trying to be perfect.