In light of the "training in secret" in Super, there's something interesting I noticed regarding the Saiyan Arc compared to the 23rd Tenkaichi Budokai. When Bulma scans Roshi and Kuririn's battle powers, thus assuring Kuririn that he's far stronger than Roshi, the Turtle Hermit questions whether or not the scouter is malfunctioning. This seems pretty strange, given he admitted that the four main humans, even Chaozu, had far surpassed him at this point, so questioning his placement in the pecking order would seem pretty strange if he'd retired from training.
Given that, do you think Roshi trained in those 5 years?
I guess it'd also give the Battle Power OverthinkersPurists a reasoning for Scouter Numbers, seeing as how it'd mean BoZ Roshi >>> 22nd TB Roshi.
Roshi was probably surprised at the gap, which was bigger than he expected, not at the fact that Krillin was stronger.