I am quite sure. I have lived in Wales a lot, visit the NLW a lot, and am working on history that has a lot to do with Wales. Not encountered one iota of trouble - except being in the pub when England got beaten by Wales a few Six Nations back
I'm welsh and have never seen this.
I studied with a Welsh girl who grew up/schooled in Wales. She despised her school for, even if it was represented as 'a bit of fun', really encouraging the kids to have a go at the English at various points. She studied in England at university level, and then in Wales also.
Why not just concentrate on celebrating the endless sporting achievements of Wales rather than deriving pleasure from England's failures?
True that, as a Welshman it has been years of indoctrination to hate the English. This pretty much only manifests itself when the rugby is on and when I get to laugh at England's various other sporting failures. Sport is great for this, it's where I get to let out my inner anti-England part.
It makes a difference if you've lived in the UK outside England. I was at uni in Scotland and it was only then that I realised how little regard people had for the English.
Why do English people find it so hard to differentiate between British and English?
I'm not saying all Welsh schools are like that, and nor of course all Welsh people, but it's an intriguing thing.
The rivalry between English and Welsh rugby is very passionate, but not aggressive in any way, shape or form. Not recently anyway (IE, not in the last 8 years since we've got more Grand Slams than them)