I'd chalk that one up to pure ignorance.
I'm sure a modder would know better but I believe the game has casting animations and executing animations as separate things, and just blends the animations when the cast finishes and the spell goes off. So it uses the same cast animation as Holy and Glare and switches to the execution animation used for Regen and such. They must've never bothered to make an actual animation for it and just went with the usual healing spell one. They probably should've just gone with HolyIII's.