Tbh, different dimension could also work in the context of hierarchy -- Shin belongs to a different dimension from Piccolo, a mortal. The ranks are too different.
Maybe by "that much, Piccolo?" Goku meant other things rather than power? "That much?", as in, the feeling of insecurity was that much? The uneasiness besides such a being was that much? And then Kuririn acts freaked out, which again could work with something other than power -- if this mysterious dude is supposed to be someone even more bizarre, more unpredictable and likely not even from this world, it stands to reason he'd be freaked out.
Now it seems that Vegeta couldn't estimate Shin's power... but is that the same as feeling no chi signature from him? What if someone argued that while Vegeta and co. couldn't sense Shin's power, Piccolo could since he obviously had more intel on Shin than anyone there -- therefore he could get a feeling for Shin's Godly status AND chi?
All things to ponderate when analysing the Piccolo vs Shin debacle.