Forgot Yamcha said that. And I guess he can sense power levels.
And thinking back I'm sure the difference in power is from Guru's power unlock back on Namek. But then Krillin never trained with King Kai.
They would still be strong enough to each other that when they fight its relatively fair with an overall edge to Krillin. But if you look at the fights they've had Tien is also much smarter than Krillin. I know it sounds like a low ball but try to think of a time when Krillin didn't use anything but sheer power to defeat an enemy. And all the examples of Tien using other means to defeat a stronger opponent.
Examples:
Krillin uses Destructo Disc and Scatterball to overwhelm enemies purely offensive measures. Infact one of his few strokes of genius was use of the Solar Flare which is Tien's move.
Tien while yes he possess a purely offensive blast is also the one to use techniques like Solar Flare, Multi-Form and Mimicry (which led to his use of Kamehameha and Mafuba).
Krillin may be stronger (whether I like it or not) but Tien's arsenal of both offensive and tactical moves is the reason he beat Goku who was also marginally stronger than him at the 22nd World Tournament.