Anyone know why these turn signals look different on this 1978 XT500, were some just that way or maybe originally from elsewhere? 

 The picture is very blurry, but doing a quick search they look just like the ones I found.

 

Probably not a US model.  Law in US was interpreted as signals needed to mount to bars to get them as wide apart as possible. 

Other countries allowed short stalks on headlight bucket. 

 Sorry about the blurry picture, here’s a little better one.  To me it looks like the turn signals attach to the headlight, which makes me think like MarkT said not an original US import.  That being said if this is the case, would anyone know if the bike would have any other differences?

Hard to say, could just be someone liked that style better. 

Get the VIN and track that down as it might tell you if it was a US model or not.