To clarify, they're talking about declared candidates only. So Clinton for the Dems and Cruz/Paul/Rubio for the GOP, who they list by name. Since Clinton gets 65% support from Dems and Cruz/Paul/Rubio collectively get just 31% from Republicans, I don't think this discrepancy is surprising.
Well, there's that old narrative about how Democrats don't actually like or support Hillary, and are just saying they do because she seems inevitable/is the only option...yet satisfaction with Hillary is higher than her actual support! So much for that.