Are these appropriate conditions for an aircraft like that?
NO!!! But that doesn't stop any number of idiots thinking it's OK. Hopefully they get scared before they kill themselves.
Would good practice be to run away in nasty conditions (as he/she seemed to be doing), or to land and sit it out?
It depends on how nasty the weather is where you're running away. Landing and sitting it out is probably safer, and certainly to be recommended if the weather was as nasty as you say. Again, that doesn't stop any number of idiots....(see above)
- What are the sensible limits for something like an R22 (or for that matter, a bigger helicopter)?[/
When I was a new PPL(H), I got told that if you're having to descend below 500 ft and/or slow down to less than 60kts, it's time to land. I might stretch those limits slightly now (while keeping the 500 ft rule), but I emphasise the word "slightly". You need to land before it becomes unsafe to try, while you can still see obstacles. But again, that doesn't stop any number of idiots....etc.
Learning to pilot a helicopter and learning common sense are two different things.
