DT swiss 370 hub ends in a thread, what is is for?
Outside of the hub, the DT 370 rear axle looks like this:




135x10, 135x10 QR, or just 135 QR, would all be accurate ways of describing the axle standard as far as frame compatibility is concerned. What can be confusing is "135x10 axle" could be taken as referring to a standard repair axle of given dimensions (in this case 146mm long with M10x1 threads) that a common cup and cone hub would use, like what a typical Shimano or OEM brand mountain/hybrid/etc hub would want if its axle got stripped or broken. Your 370, like most fancy cartridge bearing hubs, takes a specific proprietary axle with shoulders, flat machined spots, etc.
The stub of external thread is what the axle hardware threads on to, what you use to adjust the bearings, etc. It does in fact contact the frame. This can be counterintuitive, but the other counterintuitive thing is the very high amount of clamping force provided by the QR skewer. As long as it's clamped down adequately, that connection is keeping the axle from rubbing against the frame in a way that could damage anything.


Also, 9mm is associated with QR front hubs, not rears.