Hawkfish perching or captured by urchin?

[Mattyreefs]

I was at the local zoo today and saw this hawkfish that appeared to be perched vertically on an urchin. The longer I watched, the more it looked like it might have actually been stuck. Made me curious, can urchins grab onto fish the same way they do rocks, shells, frags, etc or was the hawkfish voluntarily hanging out?

 

[Sharkbait19]

I’d be surprised if the urchin actually caught it. Most likely just hanging out.