Yeah... For one, there is no way in hell that Goku would still be hyper-excited to fight a Boo-level opponent. That tier of power has faded into utter insignificance.
...Or maybe at the end of all this, the Super Dragon Balls will be used to restore the timeline back to how it was during the Boo era -- essentially retconning DBS. Lol, can you imagine the sheer chaos that would cause among fans?
Or even if it was a SSJ, it would make sense given they established Goku is happy to handicap himself. (The manga did one better and had Vegeta call Goku a dirty cheater for using god mode to deal with Trunks SSJ3 level SSJ2.)
But again: why would Goku be super-excited to fight a Boo-level character, when he's got guys like Vegeta, Beerus, Whis, etc. etc. to spar with? Guys who can give him a REAL fight -- no handicapping required.
I forget how it panned out in their fight, but as I recall Uub wasn't all that strong at the start. Maybe Goku's just excited to bring up a fighter with a ton of potential, and see how far he can bring him? In that context, Buu level would be a monumental achievement, assuming he had to work to get there..
He also had fun fighting Krillin and Tien in Dragonball, even when he'd clearly surpassed them.
Not that any of this matters. Goku references Uub in Super and calls him something to look forward to. There is no retconning. We can assume that Goku, after seeing how strong Freeza could become through all that training, naturally assumes Kid Buu's reincarnation would be even more impressive. Not only would he in theory dwarf Freeza's natural talent but all the Buu's had a pretty good aptitude for learning techniques.
His statement makes perfect sense tbh and yes, Goku did bring Uub up during the beginning of Super. Goku obviously was holding back in his Uub fight. I just think Uub potential is what he enjoyed during that fight. Uub couldn't even scratch him.