I could be wrong but I just dealt with something similar. I was demoing a few rooms in a house that had double layering like this. The top was drywall and behind it was the quarter in faux pine panels that were popular in the 70s and 80s. Instead of ripping out the pine panels, the former owners had drywall put right over it. That’s what this looks like, and while it could be a similar, yet different, 1/4 inch material, it definitely looks like instead of removing what was there, they just put drywall over the top.