>Selfdestruct does not cause the user to faint, but instead cuts its HP in half, and affects all Pokémon, items, and walls within one tile of the user, reducing HP by half on teammates, by 50 on hostile Pokémon, and destroying all walls, items, and special tiles. Selfdestruct cannot be used in rain or on any floor with a Pokémon with the Ability Damp.
There's really no reason. Your Charizard must've been a hostile Pokemon.
Source: Bulbapedia- Selfdestruct
Source: Bulbapedia- Explosion