the bottom line is that you hear about metal going crazy and people being harmed by taking metal into an MRI room… but those are the cases worth talking about. there are plenty of cases where nearly nothing happens. Survivorship bias works the other way too.
the question is - do you want to risk the potential for massive heat and kinetic energy ripping through your body because you brought an undeclared magnetic implant into an MRI procedure? probably not.
the shape of the fields in an MRI machine can be like a massive twisted up double pretzel, and the field strength can go from zero to extremely high in a fraction of a millimeter’s distance. Try holding a magnet away from another magnet when they are 1cm apart its fine, but put them 1mm apart and try it.
the point is, don’t listen to the dummies taking undeclared magnets into an MRI machine. they got lucky.