Tails like the one you show on RIG have been a trading problem since the dawn of trading. During the late 1990s when I traded Sun during the day the market makers would run all the stops at support and resitance points. I used to get some great trades by taking the contrarian trade on these tails. In todays areana who knows. It could be a single big block by a retail trader. I would be curious to find out.
It could either be a late print that your charting system plotted as a realtime trade. Or it could be a negotiated block trade, that could have either gone off through the NYSE or through another exchange or dark pool and the print was recorded at that time. Just because you see a print go off in time and sales or on a chart doesn't mean it was available for you to get filled on some shares. For a trade to get busted I think it has to be at least 10% away from the prevailing market price. But all the exchanges have been changing their rules regarding trade breaks so I am not sure if these are still the current rules. But I do believe most exchanges have a time period in which you can bust a trade, between 1 to 3 hours.