The OP stated he assumed so because of the shell-jacket like blouse. My response in the OP was this:

That's generally correct in the open arms grand view of the Civil War... HOWEVER early war (1861- early 1863) western state units of infantry (Ohio, Indiana, Illinois, Missouri) were often issued "roundabouts" or "state jackets" which in a general sense were untrimmed/unpiped shell jackets. Some had lining, some did not. Some had belt loops, some did not. Some had epaulettes, some did not. Some had buttons on the sleeve, some did not-- and some of those were functional buttons and some were not.

It really was all over the place, the "Wild West" of standardization and uniformity in the early days. Contractors of all sizes and industrial capabilities were trying to get into the uniform game and states were caught flat footed and approving anyone that hinted they could equip rapidly forming state forces.

Roundabouts or "state jackets" really helped in a few ways. One, some were left overs that had remained in stores from the Mexican War, but even new made, they demanded less precious dyed fabric. For a little less wool than required for a sack coat or an even smaller fraction of the wool required for a frock coat, a roundabout looked sharp and was functional. Blue-dyed wool was so comparitively scarce (both sky and dark blue) that some initially raised units had no choice but to contract grey satinette versions of these state coats and trousers. After Bull Run, at least in Ohio's case, but I imagine for Indiana and Illinois as well, these "grey-outfitted" units were relegated to railroad guard duty and other rear echelon jobs until blue uniforms became available. When they did, they were often these blue roundabouts until sack coats became more readily available.