Yes, it's working as intended.
On the PK7, the Met level of any VC mon, is dependent on the level it was transferred as.
So if you transferred the Mew at lv 100, the met level on the pk7 is lv 100.
It only becomes an issue if the met level is below the level the event was distributed at. (tho in that case PKHeX flags it, so also working as intended).