A-ha! All is revealed. I've never seen a bone nut that yellow before and a lot of the PBG nuts are the same yellow.
Yes, definitely sloping the wrong way for a R/H nut. But as you'll probably need to cut the string slots deeper (I use the pointy end of a round needle file for bass nuts), then you'd probably want to file the top of the nut down anyway. It doesn't need a slope, it's more aesthetic than anything, and a lot of Fender-style nuts are pretty flat at the top, albeit with a square edge on the fretboard side and a rounded-off edge on the headstock side.
Try it in place without any glue, see how much the string slots need to come down by then guestimate how much the top of the nut could be filed down. In theory the minimum slot depth is 1/2 a string (which is how DB normally cuts them), but if you ever bend the strings at all, it's very easy to unseat a string so I prefer most of a full string's depth to the nut slots on my guitars and basses.
