Disinformation alert. This person was dumb enough to have Bitcoin trade it for Monero and then trade it back to Bitcoin and send it to a centralized exchange. Monero itself was not traced. The amounts into and out of Bitcoin were traced, and then the person was dumb enough to send it to a centralized exchange to cash out. Stupid fuck.
It sounds like they went BTC -> Monero -> BTC. It's not outlined explicitly in the article, but I am guessing it's the on/off ramping that got him popped.