From the Super Mario Wiki
In Super Mario World 2: Yoshi's Island, the Official Guide from Nintendo Power describes how the Yoshi series has different enemy classes. Of those, one of them is Mostosti Vomitonus. Enemies in the class Mostosti Vomitonus are able to be eaten, and give a Yoshi the ability to breathe fire. The only members in this group are Pyro Guys and Lava Bubbles.