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You're probably misreading your doctor.
When he said "99.5 or 99.95%" I rather doubt he meant to give the precise odds. I think that what he meant was "There is a non-zero probability that the cyst will turn out to be an issue, but it is so small I consider it insignificant and so should you". Trying to base some calculations on the 0.5% (or 0.05%) chance is not useful because it's not a "real" probability, just a figurative expression.
Great point. He did seem to pause and think about it, but still a good point. It seems notably likely that you're right, and even so, I doubt that his confidence is well-calibrated.