sure enough, my jacket is in fact a XS and I'm 5'10" and the sleeves are slightly long standing, but perfect length for riding, and while it fits my torso closely, I can still put it on with a thin fleece on.
At my height you wouldnt think it would fit at all, on paper.
The caveat here is that I weigh 140 and rather slight, so this just goes to show that you must really try on jackets before buying them, unless of course it doesnt bother you that things are overly baggy.