Hey there! OpenTDB is great!
It would be great if you could use something like a license from https://creativecommons.org/ to clear up any misunderstandings.
A possible example would be Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) for example which allows us to use, adapt and share the content while giving attribution to OpenTGB:
Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
Looking forward to hearing from you