In theory this should not happen.
But for short periods I can see it happening, in certain not carefully tested systems.
The http standard includes the following actions, HEAD, GET, POST, DELETE and a url can use any of these.
The default GET is what we are talking about here, and GET requests should not actually action anything. Theory being a GET should retrieve the resource, not changing it in the process.
Of course this is not in practice followed, such as these common unsubscribe links.
So in practice urls should not be retrieved by GET without user action except in certain exceptional cases.
Even using the HEAD action may impose security concerns such as unequivocally identifying a valid email address.
Google had a pre-caching service at one point (VPN or Browser or something) that prerequested website urls to improve performance/bandwidth.
This caused certain web-apps to malfunction in similar ways to the Question.
For instance I developed a web-app around 2000 that used GET urls to do actions such as delete record an so forth, not a mistake I would repeat of course.
This pre-caching service looked at the urls and web site and inferred that it should NOT pre-cache certain links using a heuristic with inputs such as is this an authenticated site, is it https, is the url containing the string DELETE or UPDATE etc or identifying the web framework used for the site.
I dont know how accurate the heuristic was, I heard of some issues raised in this system but I dont know the detail.
Because this is a easy mistake to make on any web site (beware web coders) be very careful of implementing this feature.