Yeah, that is utter nonsense. If you use that definition you had about as many slaves in Europe alone a few centuries ago because almost the entire population would have been slaves.
“Modern slavery” is like an “honorary degree”. It has similarities to the real thing, but it isn’t the same thing by a long shot. Look at the article: forced marriage, state imposed labor, exploitative employment. That was pretty much just normal if you look at human history. What do you think peasants were?
If we really have reduce the affected population to fifty million, then we have solved 98% of the problem.