Basically, you're saying because an engine also has a packaging element (contentDB is the packaging and distribution part maintained by 1 developer, it cannot be an engine). It is both.
"Minetest is an open source voxel game engine with easy modding and game creation". https://github.com/minetest/minetest
Historically, when you install windows, it comes with a game. Does that make it not an operating system?
I'm more inclined to believe the team who make it rather than some random internet stranger though.