Bitcoin.com never give detailed/accurate news
But, most likely they meant 5% of XMR hashrate came from hijacked device or 5% of XMR coin supply was mined with hijacked device.
Also, verify total coins mined from private/fungible cryptocurrency such as Monero isn't difficult since they don't hide the amount of mined coins in their coinbase transaction.
But coins such as Verge isn't really private since every transaction is transparent just like Bitcoin.