After thinking about it more, I think I know why it seems misleading. They are talking about the change in the larger value as a % of the smaller value. That'

After thinking about it more, I think I know why it seems misleading. They are talking about the change in the larger value as a % of the smaller value. That's what is misleading. They are saying it is reduced by 90% (of some other thing). When you say "We reduced THING by N%" it's just assumed that the N% is N% of THING, not OTHER THING.