Well, why not state that to Piccolo and Vegeta then? They easily left Ginyu in the dust.It's a weird statement to throw in there, but I can't see Toriyama having forgotten so many details in a relatively short amount of time. Vegeta had just demonstrated the highest level seen by anyone who wasn't Freeza before Goku showed up.
You have to think of it from Freeza's perspective. It's more noteworthy to him that his right hand man of many years had been surpassed than Goku surpassing his own allies.