I wouldn't say those feats necessarily contradict the gap presented between Kuririn and Goku, the physcal one in specific. Not only is such a thing difficult to quantify when Kuririn and Roshi aren't exactly in completely different tiers of raw strength (Kuririn's feat of moving the rock even shocking the latter) but Kuririn was later able to make someone bleed who Goku overpowering shortly afterwards acted as a solid indicator of his strength having improved.
Goku's comment about Kuririn's reactions are a better point, but I'd say there are several factors to take into account. For one, Saiyan physiology makes them far more capable physically than humans and it's not as though Toriyama hasn't used the contextualisation of Saiyans in Part 1 to explain prior events (eg. Zenkais), so it could be assumed Goku simply has better reactions than Kuririn on equal grounds without Ki control. Alongside that, Goku had yet to fully become a master of martial arts at this point, so it would be fair to believe his estimations on what Kuririn was capable of weren't 100% accurate as he didn't really have much to go off on his friend's full capabilities when their training didn't really have much reaction focus beyond perhaps dexterity.