Flame can travel up the stream, that is not news. There are many hospital admissions every year from people trying to add some meths (ethanol + methanol, "lighter fluid" in USA) direct from bottle to the BBQ to get it going properly
The problem occurs more often if the bottle has a wide opening, then you get easy flame transfer up the stream and into bottle. The expanding gases of the flame pushes out the rest of the fuel. Very ugly!
With a smaller bottle opening this effect is somewhat reduced (hence USA "lighter fluid" sold in squirt bottle), or using a "nip" pourer on a liquor bottle. But it is still a problem
Liquor is typically around 40% alcohol, so less violent, but still very hazardous. Do what chefs do, and pour out a measured amount into a small glass (they have to account for the cost too)
Dailymail - Family suffer horrific burns from flambe