I don't interpret "business lounge" as meaning all *G lounges.
Certainly using the *A lounge finder and selecting United Club as the eligibility doesn't bring up Koru lounges (nor most *G lounges) in some random searches I tried. Looking at the United Club site makes no mention of accessing *G lounges either.
What does "business lounge" mean? That's a very good question. It's very clear it does not mean all *G lounges.
So I guess I'm asking the same question again... Where does it say anywhere United Club membership gives access to *G lounges?