I think that's a misunderstanding of statistics and the scientist is making a faulty generalization. You're only looking at the last 20 and not all of the the surgeries. Imagine the surgeon has had 10020 surgeries and the first 10000 are an even 50/50 split, but the last 20 are all successful. Would you really think you have a higher chance because the last 20 were successful?

And just for fun you can throw 10000 coin flips into libreoffice or excel and see how many in a row can be heads (1) or tails (0). I didn't get 20 in a row but I did get 19 in a row, and the statistical probability of 50.1/49.9. Something extraordinarily unlikely can still fall within the statistical average.