That's actually a cut of a longer video. What's missing is the beginning, where they stab the battery with a knife. Unless you pierce a battery, that kind of combustion is unlikely to happen. If it swells up to the point where the casing fails it could, but you'd probably notice that before it became a dangerous issue.
However, it's particularly dangerous on RC aircraft, which can crash and puncture the battery. The battery on my quadcopter fell out while 20 meters high directly over concrete and it puffed up, but didn't catch fire. I discharged it with a light bulb and buried it with a cup full of sand in my yard.
Burying a lithium battery in your yard seems like a pretty terrible way to dispose of it. Could you not take it somewhere for recycling, especially since you discharged it? Doesn't the typical AT&T/T-Mobile/Target/Best Buy/Etc store have a recycling drop-off for old cell phones and batteries?
I'm not from the U.S. and I don't want to waste money going to the capital city just to throw away a little battery. There are no battery recycling places around my village (yes, living in a village). Nor anywhere near it.