Are all DFAs also NFAs? Are all Deterministic Finite Automatons also Non Deterministic Finite Automatons?
That depends on how pedantic you are. Morally and semantically speaking, every DFA is an NFA in which there is a unique arrow exiting every state for every character in the alphabet, and there are no $\epsilon$ transitions.

Syntactically speaking, it depends on your definition: the transition function could be encoded differently, so that the transition function of a DFA might not be "legible" for an NFA simulator.

I would not worry too much about the syntactic viewpoint.