Did you read the article? I’m guessing not, because you’d have read this part

… and a “5400 RPM Class” Western Digital Red—which, as tested by audio spectral analysis, actually spins at 7,200rpm

or followed the link to the original investigation and seen this part:

Known “5400RPM Class”=7200RPM drives: … WD80EZAZ-11TDBA0 (WD MyBook 8TB) WD80EFAX (WD Red Plus 8TB) WD100EFAX/WD101EFAX (WD Red Plus 10TB) [WD80EFZX? (old WD Red 8TB)]