Acceptable flying pattern?

[dochealth]

Hi,

I wonder can anyone tell me what rules and regs apply to GA flying, please?

Earlier this evening, I saw a single engined a/c ( ? Piper Cub) flying low in mountainous terrain in West of Ireland. He was in and out of valleys at 200 ft or so.

But then pilot throttled back and descended in a deliberate swoop till he was about 50 ft above our village before abruptly climbing again.

So just curious, would this be considered acceptable flying by (a) GA community and (b) by regulatory authorities?

Thanks!

DH