The guy is sort of right. Slav is primarily a linguistic family just like Latin or Germanic. Culture has more elements to consider. There is no Latin culture because while French, Italian, and Spanish might have similar culture one can argue the cultures are Mediterranean they wouldn’t be specifically Latin since Romanian is also Latin but very different an cultures like Greek, coastal Croatian, Albanian, Cypriot, Montenegrin would be Mediterranean but definitely not Latin. Language does have a relationship to culture though but doesn’t primarily define it not to the extent something like religion does.