Well until today I didn't know that there was anyone filming Teufelsräder specifically to look up skirts, and would've thought nothing of watching a video. I've seen videos of them on YouTube before without thinking it was wrong. So I think that's how - it didn't strike me as invasive to film it, either, and given that it's an event taking place in public I still don't think "invasive" is the right description.

To me the difference is whether you're declaring that you're thinking about people sexually (or encouraging others to do the same) in an explicit way, which goes beyond filming and uploading it.