It depends on how "native" you look perhaps, but you can be detained for more than a week and a half if the border authorities don't like you: https://www.theguardian.com/us-news/2025/apr/20/us-citizen-j...

Of course they shouldn't do that to US citizens, but they also shouldn't be targetting protestors they have a personal gripe with.

I mean the guy didn’t have proper documentation and admitted to illegally entering the US (not at a crossing I assume).

It’s a completely different situation.