It's not just a reviewer at NewEgg, it's AMD.
Ryzen CPU Memory Support MHz
Dual-Channel/Dual-Rank/Four-DIMM1866
Dual-Channel/Single-Rank/Four-DIMM2133
Dual-Channel/Dual-Rank/Two-DIMM2400
Dual-Channel/Single-Rank/Two-DIMM2667
Unfortunately, many RAM providers do not publish which Rank their DIMMs are (at a guess, many 8G are single, but believe most (if not all) 16G or larger are double). Have heard of triple, but would guess not supported. CPU-Z's SPD tab will tell the tale.
Getting a pair of Double Ranked DIMMs to run at 2667 (or faster) would be considered overclocking them. AMD doesn't support, but who knows how fast the motherboards are capable of pushing the CPU?
All I know is that my pair of 16G DIMMs (32 total) will not post at 2667, even though they're rated for 3200. (using ASRock Fatal1ty X370 Professional Gaming and latest 1.55 beta UEFI (BIOS))