For the vanilla behavior pack, fireball and small_fireball have ' "catchFire": true ' within their behavior files for onHit { impact_damage { sections, setting this to false changes nothing. Additionally, if you try to add these to other projectiles like snowball or ender_pearl, they will not catch fire. Since im seeing a lot of random preference of snake case and camel case, i also tried "catch_fire", but it did not fix it.