People who make this claim are trying to make a subtle point with a simple statement, and it just causes confusion. As long as you and I cannot use the same object at the same time for different purposes, we need some understanding or rule to determine who gets to use it now and who has to wait or find some other solution. I am perfectly happy calling that ownership or property.
Even if you don't buy deontology for individuals, you should want deontology for society en masse. Utilitarianism is too arbitrary to suffice as a means of coordination.
People who use that slogan want to change the rules regarding property, rather than eliminating it.
"Taxation is theft" - now that is pretty clear.