Yeah, it seems like you’re talking about Gra’niks. There are also actual Chassidim who dress that way in Jerusalem, and as far as I know, those Chassidim actually picked it up from them, not the other way around.
“Why are they so religious and strict if they are not chassidic.”
This made me chuckle. You’re not in America anymore 😉 Statistically, Chassidim are more likely than Litvishers to work (by a big margin) in Israel rather than learn full time. Even in the US, there are Livtishe communities that are arguably more radical that average Chassidim.