It seems like the previous owner changed the angle. It could be intentional, maybe he wanted a more durable blade less prone to chipping.
It should also be noted that some people like to have a convex bevel on their chisels and drawknives. This supposedly makes sharpening easier as the curvature allows for more natural arm movement during sharpening. Paul Sellers of Youtube fame is one proponent of such sharpening. I've also read that historically such bevels were the most common blade geometry for drawknives. I couldn't find any sources to confirm that, though.
I prefer a flat bevel on my drawknives but I accidentally ground my first drawknife into that shape with a file. It took ages to get it to cut well again. It retains the convex bevel and I sharpen it by holding the drawknife in one hand, the other handle shouldered. I run the whetstone along the blade with circular motions, holding the angle as well as I can. The flat side of the blade I sharpen only to remove the burr. Were it flat, I would lay it flat on the stone, but I ruined that side too when starting out, so it's not flat either. I thus just run a whetstone as flat as possible over that side to get the burr off. works fine for the size of the drawknife.
All in all? I'd say that having a perfectly flat bevel and flat of the blade is beneficial and gives good results while allowing for easy sharpening that maintains the angle easily.
In your place I'd flatten the bevel and go from there.