I think he means that there are several algos that GPUs cannot mine which are CPU only. I've mined HODL, ROI, and a few of the Argon2d algos myself. I think it's a waste of time to try and compete with GPUs and ASICs to mine a GPU/ASIC coin with a CPU. You may as well mine BTC with your CPU if you insist on throwing money away for electricity and mining for a loss. You're better off to stick to a CPU only algo coin if you mine with a CPU. Trade those CPU coins for BTC and buy Monero or whatever coin you want in the end. It's not rocket science and you'll profit instead of lose.
Chris B.