The UN taskforce report clearly states that there are more slaves now than ever before.

His comment clearly doesn't go against that. He specifically states that that statistic arises from the fact that there are far more people alive today than ever before and the percentage (he also bolded that word) of slaves is lower than in the past.

Capitalism is inhumane. The profit margin somehow justifies the human cost.

There is no manifesto of capitalism which states that profit margins justify human suffering. Nearly all capitalist countries ban slavery altogether, while some few have it de jure banned but de facto legal (at least in some cases), and I don't know of any that have it fully legalized but I'm sure they exist.

In the end, slavery isn't caused by capitalism; slavery had been a thing for millennia under various controlled markets, state or otherwise. With how prevalent it has been since the dawn of time one could only conclude that it's human nature that will exist under any economic model and must be constantly fought against with every tool we have.

For example of other modern economic models that have benefitted from slave labor you can look at the USSR, that had obligatory labor written right into their constitution from the very beginning. On top of obligatory labor they forced 14+ million people into forced labor via the gulag system from the 30s to 50s. Most people think that the gulags were primarily to control political dissent, but released soviet documents from the time period shows that they were specifically devised by Gosplan for slave labor.