SIG is not a Swiss company it's German. There are three branches of SIG, a German Branch, a US branch and a Swiss Branch. They are owned by L and O Holdings which is based in Germany.

https://en.wikipedia.org/wiki/SIG_Sauer

I could not find much on where the XM5 was developed or by who, but it was based on an earlier design called the MPX which was an SMG, but again I don't know where it was developed.

Either way, now the US service rifle is made by a Swiss company that is no longer Swiss but owned by Germans.