I am pretty sure that you are correct on both counts, that the ATH is measured based on Bitstamp prices, which current ATH would be $4,980 (or maybe $4,979.90 or some variation of such), and I think that he has been using the UTC clock, too.
New ATH (per stamp) would be $4979.xx ... We were so close, but then there's a drop and now we're sitting at $47xx
Anything can happen because of lot FUD when the price is at $4979. Maybe it will rise again before the Segwit date because this time it is possible for Bitcoin the pass the $5000 mark with unexpectedly.