What a weird kind of projection.
Of course, had it been vertical, then the image wouldn't have included the arches, but would instead have been a bunch of pews. Perhaps there were scenes of both, and the pews turned out to be very uninteresting. Hard to know without asking.
Me too, am a fan of this kind of pinhole cams !
Here, I published a paper about the three cams that I designed and built myself,
and here, (click on the picture) you may access a galerie with a few examples of photos I took with them :
My POLKa cams have an horizontal taking angle of about 300° (4 6x18 views per 120 roll), and on the displayed picture of the rialto bridge in Venise, you can notice on both ends the same windows from a building which was actually behind me.
At the end of the paper, I show also how to watch these weird perspectives so that they look normal.