Merhaba,

how do you translate such a short phrase: nasıl olmuş ama.?

Does it make sense at all? With "ama" at the end?

Or is it just an incomplete expression?

"ama" has a different function here.It is "exclamation" when it is end of the sentence.

Google translates as "but how´s that?" assuming you meant it is a question.  I would think it could be "How was it made?!?"  But I am a beginner.

google translate s like love: its all full of hopes and promises but in the end all it did was lie to you.

if you see "ama" at the end of a sentence you can try to bring it to the front of it while translating it to english. doesnt always give the right answer but it will help you understand:

A: seni toplantıda göremedim - i couldnt see you at the meeting

B: gelmiştim ama - i cam but --> but i came

nasıl olmuş ama - how did it turn out but --> but how did it turn out?

of course the "but" there also isnt in its own english "explanation" function, but think it as its using its exclamation function.

but that was amazing! - harikaydı ama!

sorry cant think of any other way to explain