Inverted math.
Think of it as the house is
1/3 smaller and the consumption is
2/3's less.
(When he said 2/3's the size you think 2/3rds smaller)
FWIW, I've been doing the same, replaced baseboard heat to radiant hydronic, replaced all lights with LED, replaced old worn probably 70% efficient boiler with a new 89% efficient and my next step is moving from an electric hot water heater to an indirect hot water tank.