It's a large number of smaller cultures and the OP's friend just happens to fear every single one of them on their own merits.
It's the unknown, you see.
I'm not defending the OP. If you'd bother reading my posts in the thread you'll find I've been quite strongly on the side that yes it is racist.
I'm sorry that cultures don't work the way you want them to so I can't point to a specific thing because that's a nonsense answer to the question of what is a culture.
So within the context of this thread, is the way the OP used it problematic? You didn't give an opinion.
I didn't even see the OP use the phrase. All I'm saying is that the phrase in itself is not necessarily problematic. Obviously essentially everything can be used in a problematic way, context is your friend there, but some ideas are also problematic in themselves. This is not one of them.