If McConaughey campaigns as a Democrat, it’s likely that many of the respondents who opt for him now (including the 30% of the Republicans in the sample) simply would no longer consider him as a viable option. And should McConaughey instead campaign as an independent, he’d almost certainly face a Democratic opponent who would take many anti-Abbott votes from him. The dynamics of the race would also be dramatically different if McConaughey decided to run in a Republican primary against Abbott.
McConaughey himself has talked about running for governor but hasn’t taken any obvious steps towards running, so we may never find out how he’d do under any of these scenarios. However, there’s still an important lesson to be drawn here about the importance of including party affiliation (or noting the lack of it) in horserace surveys, even ones looking at very hypothetical races like this one. As we’ve written before, if a pollster doesn't include this, then they're leaving out important information and failing to accurately mimic the way voters will make their choices when they actually cast their ballots.