Packin', Rackin', and Stackin.'
Okay....
Yeah, likely the soldier didn't hear or more importantly FEEL the round chamber, and went through the sequence to eject and load (and properly chamber) the next round.
Packing, racking and stacking - first, you load your mags with all they're supposed to hold (usually minus two, because manufacturers believe in best case scenarios
) so figure 28 in a 30 round mag so it doesn't bind. If 30 rounds actually works in your mags 100 percent of the time, more power to you. Murphy's Laws of Combat always followed me, though.
Next, you rack your mags - smack each one smartly against a boot or something else solid (but not hard like a rock, so you don't damage the mag) in order to get all the rounds to rack solidly against the rear of the magazine. Having the nose of a bullet drag on the front of the mag can cause failure to feed malfunctions.
Finally, you stack your mags - put them all in place with bullets oriented in the same way, according to your own preference, but always the same way so you know which end goes into your mag well.
Anyway, if you ever hear somebody talk about "pack rack and stack" that's what it is, and the most important part is the racking procedure - getting all the rounds where they need to be oriented in the mag. This also knocks loose mags that have a "bind" in them and can knock crud loose.
I dunno about you guys, but I can always tell, even when excited, if my bolt (or slide) has slammed shut with a chamber empty, regardless WHY it's done it. My guess is the soldier in question didn't like the feel of what was happening, and let nature and training take its course. May have saved his life, never know.