That’s a good question! Not sure if I’m the best person to answer it but I’ll try! Legally speaking, I believe that both are considered unlicensed/knockoff, unless the artist has actually licensed the property or sold their work to the licensor. The big difference is that an artist is making just a few plushes with materials that have been safety tested, whereas factories are churning them out by the hundreds and bypassing safety testing. I read an article a while back where over 500,000 bootleg Pokemon plush were confiscated in South Korea.
Most but not all big companies overlook artist plushes and ‘allow’ the sales of them because it’s just not worth the effort to legally pursue every fan artist out there. The factories making thousands of bootlegs can really hurt the profits of a company so they’re usually shut down pretty quick but a lot of knockoff merch still makes it into the market.
I guess it basically comes down to what your ethics are. Some people don’t like and will not buy fanart of any type while other people collect it.
Very important please spread the word.