A positive environmental swab is a record of virus shed onto a surface; it is agnostic about the shedder. Infected humans (vendors, customers, early patients who frequented the market) can deposit exactly the same environmental signal as infected animals, including in the wildlife section if human activity concentrates there. Therefore the environmental positivity and its spatial pattern, taken alone, are consistent both with the market being the spillover origin and with its being a downstream amplification site seeded by infected people. This is why the China CDC authors describe the origins as remaining uncertain; the observation constrains where early virus was present but not the direction of the human-animal transfer.
Validity assessment — approved (checked)
Reconstruction. P1: a positive swab records where RNA was deposited, not which species deposited it. P2: infected humans can deposit the same signal (including a west-wing concentration if human activity concentrates there). Load-bearing step: therefore the environmental positivity and its spatial pattern, taken by themselves, are consistent with both origin (animal spillover at the market) and amplifier (humans seeded a downstream site), so these data alone do not fix the direction of transfer.
Evaluation. This is a modest underdetermination claim, and it is the logical complement of A-32: A-32 shows the metagenomic co-location raises the probability of an animal source (LR>1) but stops short of proof; A-33 makes the matching point that the presence/location data cannot definitively fix direction. The two are consistent — “some evidence” is not “distinguishes.” Probed defeater: does the wildlife-material co-location let the swabs distinguish after all? No, because that channel only shifts a probability, it does not determine the shedder for any given positive; a human shedding among wildlife material yields the same swab. The claim as stated (“cannot by themselves distinguish … leaving the question open”) survives. Valid.