Why progressive tense (～ている) is not used in this case?

Question

I was reading something which is supposed to mean "Why is it moving?". I would translate it as なんで動いているか？ but it actually says なんで動いてんだ？

What's the difference between them? I think I cannot capture that nuance.

I think that 動いている it's something that it's moving at this time whereas 動いてんだ sounds more like I'm stating that it's moving, but I find the lack of tense disturbing (maybe it's a very strong statement implying surprise).

Another question: Could I even say なんで動いてんだった？ meaning "why was it moving?" instead of なんで動いていたか？

Answer 1

~てんだ is just a spoken contraction of ~ている　の だ, so you have your continuous tense, and also a のだ, which is sort of an exclamation mark added to the question.