Not sure; take the case of SURG lately...
If you look at the millions of shares held by mutual funds and institutional funds, this stock should stay stable. It's average daily volume is minisule.
But, like they say, "two fools trading raises all ships", the stock moved up 10% two days in a row with light volume (the two fools trading). All ships rose.
You might be right about online trading, but I think even a commercial desk could make this happen too. I'm almost positive that if the volume were light and the price was stair stepping down, a heavyweight holder might step in & stop the play.
But, your graph is an index. That takes alot of online to affect, no?