Well to be fair it was just a fart. It's not like it was a cold decision sure it maybe a little smelly and offensive, but I would rather be farted then charged at by an angry warthog. I'm pretty it was the trio of hyenas because I recognized Shenzi's voice and scream anywhere.
Besides I wouldn't blame him for doing what he did to save himself and Timon. I don't see why he would be remorseful to the hyenas just because he used his "secret power" on them.