Bot traffic
Automated requests to a link that no person made: previews, security scanners, crawlers and monitoring.
Post a link in a chat app and it gets fetched before anyone reads the message, so the preview can be built. Send it by email and a security gateway may open it to check where it goes. Both look like clicks.
This is why a link shared into a large group can show clicks arriving before the message does, and why a link in a newsletter can show a click count that outruns the opens.
Well-behaved automation identifies itself in the user agent and can be filtered out. The rest cannot, which means every click number has some unknown amount of machine in it.