Odd trade offer by Mao

[Settler of Catan]

Decided to play on Deity mode for the first time in a while as the Americans. I was behind in technology overall but I believe I was more advanced militarily. I had an unusual trade offer where Mao of the Chinese offered Space Flight for the automobile/artillery technology.

Has anyone experienced this before? I found it odd that an opponent/CPU would almost give away a technological victory.