Property is a social construct in the sense that anything is a social construct. Like, sure, the fact that I "own" this spoon is societally constructed, but it's so foundational that almost every other aspect of human society is more abstract. Even animals have some sense of "property" - whether that's territory they defend or their stash of food. The social construct part is that we respect each other's property rights (mostly) without resorting violence, where animals resort to individual violence or threat displays.