In Latin some words of typically feminine shape can however be masculine, poeta, for example. One looks in vain for logic in natural languages which constantly change, ironing out some irregularities while creating others. We may ask why the distinction exists at all. I imagine that most people would find this quite difficult. It's easy to see how this fosters sex roles, and probably this is part of the key to the whole issue.
Natural languages have many subtle markers which put varying degrees of space between interlocutors.
I pointed out that the student was probably unaware that such a locution may be ok in the local bar, but is not to be used in written English, and he simply should be advised accordingly. These expressions give cues as to the relationship between speakers, and sometimes misfire. Whether one uses one or the other can sometimes be a matter of difficulty. Such things can be exasperating or fascinating, and that will probably determine whether you enjoy studying foreign languages, or avoid them like the plague.