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.
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.