Only a few references online to it being a place rather than a German surname.
Who said of it being a German surname? Not me, I pointed out that that this may be a germanized name of a place
and have given him Radłów, a town in Małopolskie. Radwau is d-e-f-i-n-i-t-e-l-y
a name which is not Polish in its form and never has been such, so if he speaks about "churches in Radwau", we shall try to find a Polish form of the name.
This is, of course, a hypothesis and there may be another name (or in fact another reason) which gave the base for this distortion of the original Polish name.