Could you please clarify what you mean when you say build upon?
If you're referring to altering or tracing the sprites, then yes, that is correct. But if you plan to use the sprites as assets in a game, then that is fine.
I'm not a layer, but this says I can't publish a game using these sprites, due to the "Adapted Material" definition.
NB: I'm not building a game using your sprites right now, I just came across as it's contained inside the Bundle for Racial Justice and Equality, this looked like a really odd license for materials.
Thank you for bringing this to my attention.
After reading through the creativecommons.org site and getting some further advice, it sounds like although using the sprites in games is possible, it is heavily restricted. So I'll be changing the licenses for my assets over the next couple of days after I do a bit more research.