"Jump off" as unsubscribe reason

I am tracking unsubscribe reasons for a while now. I never used to do that before.
And I noticed that ever so often the reason is:

xyz@qz.com has unsubscribed
Reason given:
“Jump off” used by subscriber, reason not requested

The first two or so instances I thought it was something cultural that I didn’t understand but I have noticed it comes back from time to time.

After some digging it appears to be when people unsubscribe without being asked for a reason ?
Is that correct ?

But according to my settings in config.php, this shouldn’t be possible:


So I was wondering, do you have an idea what mechanism is used by these people to unsubscribe ?

I did look into the history of some of these unsubscribes and while I could not find anything useful, the last one I checked contained:
HTTP_REFERER = https://mail.google.com/_/scs/mail-static

I recall once wanting to ‘spam’ an email in my gmail account but Gmail suggested to unsubscribe it instead, since it contained an unsubscribe link.
I wonder if this is the same mechanism ? But even then the give-a-reason page should be displayed when the link is clicked ?

I just tested with Google.

It appears that phplist adds the header:

List-Unsubscribe: https://www.isobuster.com/mlist/?p=unsubscribe&uid=xxxxxxxxxxxxxxxxxxxxxxxxxx&jo=1

Notice jo=1

And Gmail uses that to automatically unsubscribe when clicked …

So that explains everything.
Question asked and answered.