II understand what he is trying to convey, he just wants it to sound steeper by employing factorial math.
As such, if something was discounted 400%, it is akin to "4x the original price in a deduction".
The math may not For instance, if a product was decreased from $500 to $100, though not technically sound from a decimal standpoint, from a factoral standpoint he is stating that it went down by a factor of 4, or 400%.
It may just represent from $400 to $100 instead of 500 to 100 but you get the idea. He is taking the final value, the denominator per se, and the original value, the denominator of $400 and suggested a factor of 4 decrease, or 400%.
It is awkwardly worded and I wish he would explain it in simple terms but he probably prefers that it sound more impressive. I think him stating "a 75% decrease" works just as well rather than playing arithmetic semantics