ah...speculation. don't want to waste too much time theorizing w/o many facts, but here's some thoughts. maybe you can figure it out, i can't.
as that famous Detective Sherlock Holmes (who was actually based upon Doyle's friend Sir Robert Anderson, Chief of Scotland Yard) said:
"As you know, it is a capital mistake to theorize before one has all of the facts at hand.".
Dr. J, normally, seems rather precise and accurate, when he writes - doesn't he?
he called it a "top". pretty broad term.
no mention of "hooded", so prob. no hood - not even an uninsulated fabric one (maybe the 6oz gives this fact away also, right?)
vest = no sleeves,
pullover = partial front-zip (button, etc) [sometimes means this, right?]
sweater=pullover w/no-zip (no zip/buttons, in the UL context, right?)
jacket implies/means long-sleeves and full-front: zip, or snaps, or buttons, or velcro-type patches, etc.?
what do you think? are there exceptions where some UL Mfr calls their jacket a pullover (partial-zip) or a sweater (no-zip)? i don't know. can you think of any exceptions.
guess we might need to standardize some terminology here.
i'm guessing Dr. J said "top" b/c it doesn't, more precisely, fit the other, more standard, categories - perhaps, due to some clever design changes.
maybe a lightly insulated (over-)shirt, or something similar??? as someone mentioned earlier, could be short-sleeved?
a wrap-around with fabric half-belt to secure would prob. have too much extra mat'l due to the need to overlap, so would be heavier than the 6oz. (oh...is the 6oz size XS, S, or M? - surely not size L???)
so,...maybe we should start here, viz. what do we have to REMOVE/take-off of the Cocoon Pullover to get us down to 6oz? if we can't get down to 6oz this way, then perhaps the design, construction, or mat'ls is radically diff. than the Cocoon Pullover.
the BOLD portion at the bottom of Dr. J's BLOG sounds just a tad "frightening" (overstatement) doesn't it? to me at least, i'll have to go to DEFCON 1 (highest state of alert = "Maximum force readiness") to make sure that i take care of this piece of gear. guess, that means no warranty(!!!) other than mat'ls and workmanship. but, then...we're used to that, and are willing to accept those understandable terms, when it comes to true UL gear.