I'm puzzled (alas, a not uncommon condition recently). Earlier in the day, we had a 7.5 to 1 volume ratio of ask to bid. I counted about 750k to 100k, meaning there were mucho many more people wanting to sell than to buy.

After the flurry resulting in about an increase of 500k changing hands, the ask volume size was reduced by approx. the same amount. That tells me that the volume came off the ask, not the bid. It appears like the the numbers you're getting should be reversed because the impetus to trade came from the seller's side...not the buyer's.