He didn't damage Gohan afterwards, it was noticed by Goku. And he didn't even hit Gohan before the speed increase, Gohan blocked his kick attempt. Goku said "stronger" too... I think he evaluated Dabura's strength separately to his magic. More like a "he has magic and is way stronger too".
Even if you want to assume that Goku's quote about Dabura being "way stronger" was strictly about power, there is room to maneuver.
Chapter: 450 (DBZ 256), P2.5, P3.1-4
Context: after Kaioshin again warns against unleashing Boo
Vegeta: “Hmph…The way things are going, this ‘Majin Boo’ guy isn’t going to be anything special, is he? Just like that ‘Dabra’ jerk…[ ] I’m saying that this ‘Dabra’ guy doesn’t seem as bad as you two feared. Looking at his attacks and movement outside earlier, it seems that if we just watch out for his spit, then we should manage something. I can’t call Kibito anything but a bumbler for getting done-in like that…”
Kaioshin: “…Is-is that true, Son Goku?...”
Goku: “Yeah…Well, even if that wasn’t him at full force…I think that before he would have been a frightening opponent, but…7 years ago there was a guy called ‘Cell’…[
Dabra]’s probably about as strong as him…”
The initial estimate of Dabura was as vague as it gets. If you have an issue with him being Cell @ Goku level then the quote allows for him to be lower by a decent margin.