While I don’t dispute any of the comments about Google’s attempts to make money any way it can (after all, they could easily write their own system to not allow more than one charge when impressions are less than clicks, but I digress).
There are a few use cases in which this can happen. Most notably would be if a user clicks on an ad, clicks back and reclicks it, I believe that results in one impression (the page is loaded out of cache) but two clicks. It can also happen if someone saves a URL that includes a GCLID query parameter in the URL and then returns to the site via that URL.
Also doesn’t take the sting away but I’ve seen this happen often enough over the past 10+ years of ads management.