So, did they go to MED 1?
SQ221 often (If I'm thinking right) has curfew "fringe" dispensation and can land between 5am and 6am on RWY 34L; but at MED 1 status I suspect they can land before 5am.
I would also suspect if they were closer to AD or ML than SY, declaring MED1 would initiate a diversion; so it's possibly a little more complicated than just saying "affirm MED 1". But if it truly were a MED 1 scenario and they didn't declare and divert then they could and should IMHO be found to be negligent.
The only thing that has higher priority than MED 1 is another MED 1 in front; usually we give as much track shortening as safely possible and cancel all speed restrictions etc.