> Does that logic apply only when the claimed cut is over 100%?
Yes, I’d say.
It’s the same as the informal usage of “X times smaller” to describe scaling by 1/X. The idiom generally isn’t used unless X > 1. (The exception might be when several values of X are reported together. Then one might say “0.74 times smaller” to maintain parallel form with nearby “4 times smaller” and similar claims.)
You ignored the 2nd part of their message, imagine this:
> We cut prices by 50%! Before $30, now $20
Would it be pedantic to call that price cut bullshit?