Rather than attributing to "fat finger error", one possibility on the 200,000 share sale at 3:33PM yesterday is a margin call that must be made whole by 3:30PM. That sale dropped the price from $305.37 to $300.20, and then SP quickly recovered.
Here is an example from past history on large margin calls: >> "The stock sales help to explain an over 14% drop in Valeant shares on Thursday on seemingly little news." Valeant CEO Michael Pearson Sells 1.3 Million Shares After Margin Call On $100 Million Loan
Pretty sure it was a simple, knee-jerk reaction to the WSJ FUD headline that hit right before the drop.