Incompatible armor for merc

I recently hired a Moulder Strike, whose attribute is STR, but when I try to put a Garb of the Ephemeral, which is a STR/INT body armor, my merc can't wear it.

As I searched on poe wiki (https://www.poewiki.net/wiki/Mercenary), it says that this merc can wear STR / STR and INT / STR AND DEX gears. Is it a bug, or I am missing something?

Despite the str requirement, the base item is a savant's robe, a int only item.