Actually' I've come up with a simpler, more likely explanation. TDA is scamming its customers again. Still, I think that dump last week was ALL ALGO TRADING.
I'm currently thinking that the data anomaly on Thursday was a result of TDA having "streamer issues" - which puts their retail clientele at a disadvantage. Noticed a "streamer is down" message when I visited the TDA site right after close yesterday. I've experienced this sort of thing TDA before, should have thought of it right away.