Ooooh....good catch, I take back my no way under 120 lb comment!...sorry. Typically combos come with a very adjustable "one size fits all" binding but maybe this has a kids or ladies binding on it. Slalom binding sizes are often labeled S, M, L, XL etc and its typical to list a regular shoe size range that it will fit such as 10-12. I've seen some combos skis labeled this way as well I guess. If it really is size 2-7 and not a typo then I still question why they would be on 67" skis...seems 65, 63 or smaller would be more typical. I've never seen a binding range go down to size 2.
I definitely wouldn't order w/o a phone call now and even then the chances of really finding out are probably small. It would explain the deep discount though!
EDIT: From memory and the pics (check
here ) I believe the "one-piece" refers to not having the 2 piece adjustable length like typical combo bindings had. You know, where you pinch two levers and slide the heel back and forth. This is one piece, but the forefoot overlay is split and put your heel to the back and then you wrap the split pieces over your forefoot and secure w/ velcro. Seems like a neat idea to hold your foot pretty secure, but I haven't tried it.
Actually I found a better picture that shows it clearly:
The size chart in the link above doesn't match up at all w/ the ad...they show XXS 2-3 or S 6-7 among others. I'm also surprised by the the tight shoe size ranges for this binding on the website.