Note the chart you show (which I presume is from Helen, is titled Up Volume as a % of total (rather than just down vol).
That makes a difference. Unfortunately there does not seem to be a total vol figure on stockcharts you have to manually add it up. i haven't got access to the historical data so can't calculate the MA but the figure for today at 74.5% is pretty high relative to her chart. However that may mean nothing.