I'm sure he is talking about the copyright and artistic property, not particular 3d models themselves. Sharing available assets is not a problem but making and using assets of others may be, like using a model of the portal gun, which is valve's property, like op said.Bro, VNs reuse the same generic assets over and over and over. They're not necessarily ripping from one another. You can see that same ugly haired badik protagonist in every game, that park with iron railing is literally in like 90% of games and they just keep reusing everything. Some of the devs get credit for being the authors, even though it is not their creation.
Oftentimes, it is just downloaded from the same copyright free database, bought from the same asset stores and modified using the same software.