Looks more like Infantry crossed rifles, to me - and the Infantry Blue hat cord will photograph 'light' - making it appear as Cavalry Yellow in the old photos of the era.
His Discharge will have his unit of assignment - look for his Record in a small, black oilcloth-bound booklet.
If you're going to do the Punitive Expedition, the M1917 wasn't issued to US forces until 1918 - and all of the shirts were made of wool.
Time to start looking for a replacement M1903 finger-groove stock.
Scouts Out!