Freeza oneshots. The fact Coola later says Super Saiyan is what must have defeated Freeza makes it apparent he likely thought Goku killed Freeza in a lower form when making the two other comparisons. The first time Coola notes that he can see how Goku defeated Freeza is when he was able to counter his eye laser even when getting hit, despite it being a casual attack from a Coola who's Ki had yet to surpass his brother's peak. It's not as though Freeza getting to full power would be a quick task, either.