I never said he was a star, I never said he was well known to casuals.
I said he was a champ in multiple weight classes and multiple divisions--with title defenses--and had already earned million dollar purses. His bones were made.
When Conor contacted him (and if he was a chump, why would McGregor do that, in the first place?) Paulie had already retired with a net worth in the millions. Conor became a "global star" by crossing over for the Mayweather fight. He was known to MMA fans, but you would have gotten your same "blank looks" if you asked a mainstream person about him in 2015. So yes, casual fans probably wouldn't know him. But McGregor did, because he has similar size and handspeed to Floyd, and knew he was a quality fighter.