Fish Food > Turned To Powder Plus ? Hatched Baby Brine Shrimp

This morning, I unearthed a tub into which I had combined various flake and pellet fishfood that were less favoured by my gang.  The tub probably hadn't been opened for a year, possibly even two.

I opened the lid, only to find tiny little insects (1mm in size) scurrying all around. 
The fish food itself was unrecognisable, having turned into a powdery form rather than flakes and pellets as had been labelled carefully on the outside.  The tub was in another container, untouched also for this duration, so there is no way that any jostling would have occurred (and thus which would have accounted for the powdery food). 
I assume that what must have happened is that any egg-based contents were in ideal conditions to hatch, and then the insects were feeding off the fishfood itself, accounting for its pulverised form.

Instantly, I discarded the entire container and contents.  I would have taken a video/picture if able to but I didn't want the insects escaping any more than they already were.

Has anyone else had a similar, or other unexpected, experience in fishkeeping?

Had a quick internet browse - seems the powder wasn't the food but the colony of the insects! 

This photo ( from another site https://www.fishforums.net/threads/tiny-white-bugs-in-fish-food-help-identify-please.446531/) of brown powdery stuff in the fishfood is exactly what I thought was my pulverised fish food - but that's all I could see, with lots of the little creatures escaping the tub. Instead, it seems that it was an entire colony of likely thousands of flour mites that must have been covering the fish food.

Fortunately on two counts, I closed the container before too many escaped, and made a last-second decision not to empty the contents into the food compost bin and the container itself in the packaging recycling bin.  Had I not done that, I dread to think what sort of infestation this would have evolved into!

Useful info here: https://www.wikihow.com/Get-Rid-of-and-Prevent-Flour-Mites