That’s an example of the logical fallacy “too few alternatives”.
There are other possibilities.
Sure there are! Maybe they thought the vaccine was dangerous and were suicidal, but then it wasn’t.
Maybe there’s someone sneaking around mugging people and forcing them to get the vaccine, and the people being mugged are too embarrassed to report it.
Disappearing ink in the right places?
Chinese agents in the statistics offices trying to make us more complacent?
Any number of possible reasons for the “first acceptors” not to be heroes at all.