That surprises me. I would have thought the odds would be more like 80 to 1 in Mayweather's favor. Conor must be a better boxer than I have given him credit for being. I am a big fan of Conor but I don't want him to beat Mayweather. The MMA fans would then claim vast superiority of their sport over boxing.
Outside of Berto, that's better odds in favor of Mayweather than anyone since Henry Bruseles (where he was -2000). It's a very wide skew in his favor.
That being said... if you believe these odds, McGregor has a 5-10% chance of winning. I think it should be much less than that.