Samson Oak received a Vulpix egg from the Kanto region from his cousin, Professor Samuel Oak
and he brought it into the Pokémon School classroom to show it off. He didn't analyze the eggs to see what they were as he thought it's much more fun to wait for it to hatch.
He had two eggs and he asked the class which one they wanted to raise and he would raise the other one. The class chose the egg discovered up on Mount Lanakila and he kept the Kanto egg to raise. In SM14, it hatched from an egg into a Vulpix.