They probably brought their phones, and walked by some cameras along the way (aren't Teslas covered in them*?)
Either would be enough, and I wouldn't be surprised if they parked nearby, too.
* - That cybertruck doubles as a surveillance van with footage that is shared with authorities for persecuting/prosecuting people. Expect it to be used against opposition protestors, those who seek abortions, etc.
I don't favor Musk at all but I find it hard to believe that the nazi salute was on purpose, seems like that was blown out of proportion, but the chances are not zero, Musk grew in Pretoria, South Africa which had an Apartheid Government with similar ideology, a place which a lot of nazis took refuge after they lost the war.
You might say Musk might be too busy playing video games to actually have read up on the subject. He might be more of a hanger on. But the Germans would've charged him with a crime for what he did. They know what they saw.
Try not to salute any Nazis on your way to the parking lot...
Musk did it deliberately, he did it with gusto, and he did it twice: https://www.youtube.com/watch?v=smQNNo2a9xc
It's who he is. It's who he wants to be.