I’m not trying to defend this arrest, but that’s not really how it works. If there’s an obvious illegal motivation for doing X and the person who did X can’t supply a plausible alternative explanation, then a jury may conclude that X was done with the illegal motivation.

Say that I take an item from a store. That’s only a crime if I did it with the intent of stealing it. But the prosecution doesn’t really have to “prove” in any practical sense that I had that intention. If I don’t have a plausible story about why else I did it, then I’ll probably be found guilty.