I am not able to determine if this article is good advice or not.

It makes sense that having different (VoIP) telephone numbers for different categories is good op-sec.

But the logic of not being traceable because your SIM card happens not to have a phone number is bonkers. The persons who want to spy on you might start with the knowledge of where you were at some point in time and compare all the cell tower data in the vicinity with another time and place where you were known to have been. The SIM-card with data-only that was at both time and places is you. So you’re still identifiable. It just take a bit more effort but that’s all.