The spell is the same level as the slot used to cast it
The PHB says:
Casting a Spell at a Higher Level
When a spellcaster casts a spell using a slot that is of a higher
level than the spell, the spell assumes the higher level for that
casting. For instance, if Umara casts magic missile using one of her
2nd-level slots, that magic missile is 2nd level. Effectively, the
spell expands to fill the slot it is put into. (PHB 201)
According to the rules, an upcast spell counts as whatever level the slot used to cast it was. There's no difference between slot level and cast level on a cast spell.
Thus, melf's minute meteor cast at 9th level is a 9th level spell and will not be able to be used with contingency because contingency requires that the spell, as cast, be 5th level or lower.