It's just his opinion. I think the definition of opinion says it doesn't have to based on any knowledge or facts.
Hmmm, interesting distinction. Maybe we need a new word to describe an opinion that's based on knowledge or facts, because as you say the old word "opinion" might mean something else now. This is how English evolves, I think. You may be onto something, maybe you're making linguistic history.
As a further and timely example, as per an earlier post Trump seems to have declared that the pandemic is over, although I suspect that what he actually said, as in which precise words he used and in what order, might mean something completely different as they have done many times before. I am no authority on that, that's for certain. We may need a new definition of when a pandemic ends or a new word to describe when it ends in one person's mind, as opposed to when people stop getting sick.