Personally I think that if 'facts' were noticably easier to prove in Physics then we wouldn't have consumed the last third of a century of physicist brainpower on String Theory (et al), blocking students of competing theories from funding/tenure, with no useful results to show for it. The stuff that's easy to prove has broadly already been proved... but... I don't think that's relevant.
People have confirmation bias regardless of being shown evidence, it's the central feature of confirmation bias that you interpret new information in a way that supports your pre-existing view. It's a human trait not a feature of the subject matter.
You: but he's a physicist, in biology things are harder to prove
(the point is that people have confirmation bias even when things are 'easier' to prove)