That is not evidence that people have never been magnetized by the vaccine.
Provided above in the BBC link where an expert in the field explains why that is not possible.
I have also shown how magnetic my arm is. In the wrong arm. With coins that aren't magnetic. Again, the BBC video explains that too.
The evidence is - there is no mechanism by which a vaccine could cause someone to become negative, some of the "evidence" of magnetism is easily reproduceable with non-magnetic objects and the only sources showing evidence for magnetism are known quacks, deluded people or liars - the BBC deals with that too, one woman who posted a fake video as a joke, started to "go viral", ironically, and took it down as she hadn't intended to mislead.
In brief: Not all evidence is created equal. You only consider evidence credible if it backs up your position. If you do that then you can "prove" any ridiculous claim.