9 Hole Differentials in WHS

So it's because some good scores dropped off my handicap so my 46 yesterday is a better score because my 9 hole handicap was 10 instead of 9 like it was on the previous?

Could be.
A small increase in 9-hole course handicap can reduce the handicap used for the scaling up 9 (when the 18-hole handicap - which isn't displayed anywhere - doesn't change) and result in a lower differential.

It's not that it's a better score though - it's the same score.

The lower SD is an anomaly of the chosen methodology that makes zero sense (although it would have made sense under the old system), but will be a thing of the past come April, when the calculation changes to use expected scores.