Even in ordinary times I'd wonder, what the limits of spiritual jurisdiction are.
But its weirder in SSPX type situations because those priests and bishops, by their own admission, don't have ordinary jurisdiction. So I don't think Bishop Williamson could really order Matthew to do that under pain of sin, and I don't think he'd be obliged to obey (though maybe it would be more prudent to do so, he'd have to decide) if he did.