Wouldn't this also mean that the exact same poll shows that 50% of Biden voters think Israel is NOT committing genocide against Palestinians?
No, people can be undecided, among other possibilities. The very important unknown here is how the poll question was structured. That 50% can mean
wildly different things, depending on what options were given in the poll, and how those were tabulated to get 50%.
Imagine if the question were, roughly, "Do you think Israel is committing genocide against Palestine?" Definitely not the way the question would be phrased by a professional who is good at their job, but for the sake of a quick and dirty example I'll go with it. Now imagine different ways that people are given to answer that poll:
Type A:
Type B
- Yes, they are committing genocide
- No, but they are committing other war crimes
- No, Israel is acting within the law
- Undecided
Type C
- Strongly Agree
- Somewhat Agree
- No Opinion
- Somewhat Disagree
- Strongly Disagree
Type D
If 50% of people say Yes to Type A, while 40% are Undecided and 10% say No, that means something very different than 50% Yes, 49% No, and 1% Undecided.
Type B makes for even more interesting results at 50%, if a large portion think that "genocide" is an icky word, but that war crimes are definitely going on. 50% genocide and 30% other war crimes would be a lot more damning when you think aobut how reluctant some people are to use the word genocide, especially when given other options.
Type C might be underestimating the 50% if they only include Strongly Agree and don't count Somewhat Agree.
While type D could be wildly reaching for that 50% number if they counted any answer other than zero as being belief that genocide is happening. (And there are real life examples of poll interpretations being skewed this way. If you've ever seen wild headlines that some high percentage of college age men think that rape is okay, it's because they were asked something like "How acceptable do you think it is for a man to demand sex after paying for dinner?" and any answer other than completely unacceptable was then translated into "thinks rape is okay".)