> ... does every fact need to be cited? 

Generally, you do not need to cite information that is considered common knowledge. For instance, facts found in many sources or facts easily observed.

> if I were to say a PTM is a type of NTM, would this alone need to be cited with an in-text citation?

I would say no. Even [Wikipedia][1] is already aware of such. But be aware that your argument might be stronger by using supporting evidence from other sources. Additional information related to the topic you're discussing would help to verify your claims.

  [1]: https://en.wikipedia.org/wiki/Probabilistic_Turing_machine