Can you elaborate on how any sort of backdoor could be hidden in the model weights?

It's a technical possibility to hide something in the code, but that would be a bit silly since there's not that much of it here. It's not technically possible to hide a backdoor in a set of numbers that are solely used as the operands to trivial mathematical operations, so I'm very curious about what sort of hidden backdoor you think is here.

I'm trying to think of what kind of adversarial 3D model the weights could produce. Perhaps a 3D goatse?

I mean... you can just firewall it?

Your concern is reasonable.

According to DOD, Tencent - which published this model - is a Chinese military company

https://www.bbc.com/news/articles/c9q78wn9g8zo