I think the Welsh have had a tough time keeping hold of their language and culture amidst the influx of English holidaymakers and ex-patriot home buyers. It's of little wonder then to me that they can seem a bit dour and unfriendly, so yes I have experienced this.
Personally whenever I go there I show a genuine interest in the language and culture and when I next go I'll make the effort to learn a few words and phrases. So far I only know "diolch", and how to pronounce Lllanfairpwyllgwyngyllgogerychwyrndrobwllllantysiliogogogoch (that was from memory btw so not sure if I spelt it right).
I love Snowdonia.