In my opinion, it most likely was one of two installed above the artificial fireplaces installed in many bungalows. My mother has a Chicago Bungalow style two-story that she has been living in since he father had it built in 1926. Each floor has an artificial fire place in the front room (or "frunchroom" in Chicagoese), and had two leaded glass windows above it, and no storm window. The frames deteriorated, and the glass leaked air near the lead.
I remember my relatives saying that in the winter, the fine snow would blow in between the lead and glass on days when we had a mean North wind. Also, since no storm glass, the leaded glass would sweat and freeze. I remember seeing frozen crystals on these windows in the 60s. So...they had the windows pulled out and bricked up to reduce the cold air, ice, and subsequent water thaw that went with it and left a mess on top of the fireplace. Some folks put the glass in the attic for storage....and folks like my parents threw it away (gasp!).
How awesome that you have a beautiful, rescued piece of glass from that era!