I think I might have to write something specifically addressing this misconception because a few people seem to have picked it up.
I think our disagreement is to do with our differing usage of “evidence”, not a misconception. I’d say that a sole anecdote of someone seeing Russell’s teapot can be considered evidence for its existence, even though it’s not credible evidence.
It’s only evidence for the existence of Russell’s teapot if more people say they have seen it than you would expect in a universe where Russell’s teapot does not exist.
I would add that different situations require different standards of evidence, depending on how willing we are to accept false positives. The fire service only requires one phone call before they respond.
As the word evidence is commonly used, there is evidence for Russell’s teapot—just not evidence that you or me believe in. If someone says “Russell’s teapot exists! I’ve seen it!”, that is anecdotal evidence for its existence. Anything that suggests something is true or false is evidence, no matter how flawed that evidence may be.
It is by considering all the evidence, for and against our beliefs, that we progress towards truth.