Like the entire "hurr British food bad" meme in general, it was just made up by Americans who have very little knowledge of the going on of things outside North America.
I'm gonna get crucified for that statement, but it's true.
You're right, British foods are typically baked, fried, or roasted. I really don't know where this idea of boiling stuff comes from. Boiling is actually something I find unusually rare in British cooking.