Heated up oil for frying, stirred it, tiny bubbles appeared and rose slowly but with very loud popping sound - why?
It definitely sounds like you had some water on whatever you stirred the oil with. When water droplets get in the oil, they sink since oil is lighter than water. Then the water droplets turn to steam because the boiling point of water is much below the boiling point of oil. At this point, the steam rapidly rises out of the oil and escapes with a noise and a splashing of  oil.

It's good to be aware of the temperature of your oil when deep frying, but the oil will start to smoke long before it spontaneously combusts. Use a thermometer, and know the smoke point of the oil you are using, and you will be OK. The real danger is oil touching the burner, or the oil spilling on you, rather than the oil in the pot exploding. Stirring is unnecessary because the density of oil reduces as temperature increases, allowing the hotter oil to make its way to the top (but in a nice controlled manner, unlike water).