Whatever Rin may be referring to that's classified Alphinaud as an "Elf," it must be physiologically similar to his race. Furthermore, his assumption is... indeed correct, although that's hardly something limited to Elezen of his world.

"I am studied in the arts of summoning magicks," he agrees, a curious tilt of his head as to why that was an easy guess for him to make. But more pressingly, Rin has introduced himself, and as such, Alphinaud should extend the same courtesy. "I am Alphinaud Leveilleur, hailing from the realm of Hydaelyn. It's a pleasure to make your acquaintance as well."