This doesn't mean shit.
Conor is naturally a big guy, his natural weight class is LW and he used to basically kill himself to get to FW. Now he's moving to 170, he has to bulk up and add more muscle instead of losing as much weight as possible. Of course he's going to look huge. When you're naturally his size already and have to actually gain size to fight at a bigger division, you're going to look a lot bigger.
Conor is clean. I could never see him as a cheater. He's seriously against steroids and people who use them. If he wasn't, then he wouldn't have reacted the way he did when Nate said he was on roids. People who are on steroids wouldn't react like that if they were accused. Conor is one of those guys who is really outspoken about it, more than others. He hates that stuff and people who use it.
He hates cheaters. He's natural. Just because he's a big guy and looks huge compared to how he usually does since he doesn't have to cut like 30 pounds doesn't mean he's on steroids. Conor basically gets to fight at his walk around weight and he's fucking huge at his walk around weight. Just look at him standing next to GSP.