Technically, my Quirk counts as one power. [though he can see what Rin is getting at] But Quirks don't always manifest in that way. Sometimes, the child will just get one parent's Quirk. Or, in extremely rare cases, it's possible to get a new Quirk that is entirely unrelated to their parents' Quirks.

[also, he knows his father is kind of... awful... to arrange for a Quirk Marriage just so his child could pass All Might in power]