Originally Posted by uki1234

"Piccolo didn't watch the fight, he only sensed two powerful chis fighting."

Those chi's were on similar level, otherwise Piccolo wouldn't ask the question he did. So Goku wasn't at full power while he was fighting Fat Buu.

No.
Goku(answering to Vegeta) said that he was trying to kill Kid Buu, but he just couldn't do it, cos he couldn't reach full power.
Vegeta also said that with his SSJ3 power Goku should be able to kill Kid Buu in an instant.