From the view of the law in Austria 
Upload / giving them to other people-> against the copyright
So when you give the assets to someone else or when you upload a project that contains those assets -> against the law (but when you get caught, you dont have to pay so much like in the US or Germany ^^)
**Download for personal use -> not clear if it is against the copyright, but a private copy is legal **
So when you just download the assets to learn from them without giving them to someone else -> legal
In most other countries it is like that 