Congratulations to our presumptive Democratic nominee, Joe Biden!
That's not right. The poll says 22% of the Fox viewers who expect to vote in the Dem primary support Sanders. That is not at all the same as saying that 22% of the viewers of those three outlets who support Sanders watch Fox (and that only 16% and 13% watch the other two). That's flipping the correlation backwards. It's as if you read that 5% of the people on DU were from Canada, and therefore concluded that 5% of the people in Canada were on DU. I hope you see why you can't flip things that way. It's a math thing. 
As for the other points...
Yes, we're talking percents, not raw numbers. But, so...? The percents still tell you that, in raw numbers, almost twice as many Fox viewers who expect to vote in the Dem primary intend to vote for Biden compared to the number who intend to vote for Sanders. Since we don't have raw numbers, we can only make that kind of statement within a given network's viewership (because they are all some percent of the same unknown number). We don't know, in absolute terms, whether in this survey it is the MSNBC or FOX viewers who include a greater number of Biden voters than the other (or greater number of Sanders voters than the other). Maybe that data is available in the poll's supporting docs. But I don't think that info is relevant to the points either of us is trying to make.
As for whether Fox viewers who are voting in Dem primaries are choosing the candidate they would actually prefer over Trump, or choosing who they think Trump could more easily beat, we have no way of knowing, regardless of whether they picked Biden (as the largest group of them did) or Sanders.
If I were to vote in a presidentialprimary today, I would vote for: Joe Biden
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