You understood what they meant, though. But yeah, it's confusing. I argued with my PhD advisor over this several times. "50% slower" or "10% slower" is ready to understand, but "96% slower" is harder to figure out, and it's easy to dismiss the difference between 96% and 98% because the numbers are similar
As far as I can tell, this is an aspect of language which people merely pretend to have problems with, out of pedantry, rather than a barrier to understanding in any possible case.
Everyone understands that if A is 2x faster than B, then B is 2x slower than A. If you say either of these things to someone with a basic grasp of sums, and then tell them A takes one second, they'll know that B takes two seconds. It doesn't matter which one you supply. No one would get this wrong.