I find it hard to figure out. DS8 has done the same thing and has vision issues and was an early whole word reader despite his vision. I know assessments penalize accuracy much more signficantly as grades go up (third being a big jump off if that sort of teacher led assessment is being used.)
Instead of a finger, just using a bookmark or playing card to track the line helped DS. I found some website showing an adult using a card to help learn speed reading and that persuaded him it was cool to do.
Having a similar vision issueto DS, some time when I was a kid I started subvocalizing when I read which tends to keep me spot-on word for word reading. However, in typing I often skip words.
But it seems like speed, reinterpretation, vision tracking, whole word/pattern readin, could each together or individually contribute. I would think in your case, I'd give it time to see where he goes with it.
