Did Goku lie about Super Buu?

[Totamo]

Goku says that he couldn't beat Super Buu, but Gohan could, but when Gotenks unfuses and he is Buuiccolo, Goku says he can beat him. But that form is stronger than Super Buu, so what gives?!

[Kaboom]

Goku says that he couldn't beat Super Buu, but Gohan could, but when Gotenks unfuses and he is Buuiccolo, Goku says he can beat him. But that form is stronger than Super Buu, so what gives?!

I'm like 99.999% sure this is a dub-only line you're referring to, where Goku tells Piccolo-Boo something like "you don't expect to beat me like that, do you?" In the original, Goku just remarks that Gohan can now handle Boo again, not himself.

That hopefully settled and put aside... no, there's no indication at all that Goku was lying about Evil/Super Boo being too strong for himself and Vegeta to fight. We know he was lying about Fat Boo because he later admitted it, but there was no such admission or retraction from him regarding Evil Boo. Which is why the anime's treatment of Pure/Kid Boo, whom Goku can fight and feasibly beat, as the strongest form of Boo is so baffling and contradictory.

[LowRyder2005]

Bear in mind that, purely in theory, it could've signified that Buuccolo was weaker than Super Buu as well. However, the line in question is both an anime addition and Funi's own work. It was not present in the original Japanese version, in which Goku simply states that Majin Buu has lost a lot of power and that Gohan can beat the newly-formed Buuccolo. More or less a transliteration based on what Goku says in the manga.

You can see the scene for yourself here: https://www.youtube.com/watch?v=IgJe8_uN1hk.

[cheddarsword]

Goku says that he couldn't beat Super Buu, but Gohan could, but when Gotenks unfuses and he is Buuiccolo, Goku says he can beat him. But that form is stronger than Super Buu, so what gives?!

Note: The original dub has countless inaccuracies. Watch Kai. Best advice I can give here.

[Darkprince410]

Goku says that he couldn't beat Super Buu, but Gohan could, but when Gotenks unfuses and he is Buuiccolo, Goku says he can beat him. But that form is stronger than Super Buu, so what gives?!

As Kaboom commented, that was only within the Funi dub of Z. In the original manga and anime, Goku doesn't make any comment about his own odds of fighting Buu, but rather that Gohan could beat him in that state.