Looking at the scope since threads do not extend all the way out I wanna say they are not threads but simply grooves to cut down tube glare. Rather than having a smooth surface it is grooved to not allow light waves to bounce evenly into lense. Instead they are stopped by grooves.
That and it also may have something to do with construction method.
Either way if you look at below pics of solar cap on an old Tasco Pro-Point that I have you can see threads extend out all the way.
Also look at first pic of aimpoint Comp M4 carefully. You can see how threads rise out and would engage a smaller diameter tube attach. Second pic of eyepiece on M4 you can see threads extend all the way out.
This is only way a cap or attachment would ever attach to anything I ever saw.
Since outer edge is rounded unless threads/grooves stick down lower than smooth part I dont see how anything could screw to it ? You would score the smooth part trying to screw anything past it, no ?
I cant see from pic if the threads/grooves rise out farther than the smooth part ?
Either way that is a super durable and very nice optic you have there.
That thing is simple and battle ready as intended by its makers.