Overkill killed it with a good answer.Agreed but the filter Mag should be catching a lot more of the iron if it was doing its job I would think.
UOA is/are (basically) metals in solution. In solution means not sticking to a magnet - that is A) Hot and B) on the other side of a steel wall (can).
Never seen a magnet drop Fe in a PCMO UOA even if, somehow there was a perfect before and after way to replicate showing"lower" Fe.
Nice thought but not real.
EDIT: NOT saying magnets don't work or don't have their place on drain and sometimes fill plugs in diffs, MT's etc