This usage of "a couple" is so common that it's far beyond some weird thing some people say, and telling a non-native speaker it's wrong is not doing them any favor - it's basically universally accepted usage. FWIW, if you have a reference to a styleguide that explicitly addresses it I'd be interested - I did a short search and didn't find anything, but I also don't have easy access to the full text of some major ones. But even then, disagreeing with some style guide doesn't make anyone "illiterate", or "needing english lessons" (which by the way explicitly teach people that meaning of couple, because you need it to understand English in practice).

(and I didn't flag your original post, because I don't think merely being wrong justifies flagging)