Welcome to the forum. I hope you'll love your 950 as much as I love mine. Now, for my humble opinion on your questions.
The red dust is not a good sign. However, 10 years and 30k+ miles could have something to do with it. Can you move the washer behind the nut at all? You should not be able to, but when mine went loose on me, I could wiggle the washer with my finger. If you can move the washer, your nut needs re-torquing. If you catch it in time, the only parts you'll need are the washer (new part number now - not sure if this was the cause of this issue or not, but...) and a new nut. If you wait too long, the pulley then the shaft can be damaged. If the belt hasn't slipped, it is likely OK.
Sorry, but I really could not hear any noise in your video but suspect it might the pulley moving on the shaft if indeed the nut is loose. Mine belt tracks in the center of the front and to the outside edge of the rear when everything is set properly.
Everyone has their opinion on belt tightness, but almost everyone agrees the service manual recommendation of 5mm is too tight. I run mine at 10mm and have no issues. Then again, I almost never go full throttle. I do have some fun on occasion with no slipping, just not full bore every time I take off.
I'm sure some of the more experienced forum members will chime in with more advice. I've only had mine for 4 years & 28K miles and am on my 3rd belt. Long story and I'm tired of typing. Suffice it to say I was a victim of road debris (I'm lucky that way) AND the dreaded loose nut from the factory on a new bike.
Good luck and keep us posted on progress.
You're never really lost on a bike. You're just riding somewhere you haven't ridden before.