I don’t think he said he is pasul for eidus, rather as mesader kidushin, he decided that he does not want this operson as an eid. Which as mesader kedushin seems to fall within his purview.
If that’s the way it happened, I would agree with you (although, were I the mesader kidushin, I would have investigated these things before the chuppah, rather than potentially embarrassing someone at the wedding itself — but that’s not the point we’re arguing). However, it’s reported that he disqualified him, not asked that he simply be replaced with another.
The Wolf