Looks like sugar crystals.......
Some honey will crystalise faster than others. It depends on the fructose/glucose mix in the nectars collected by the bees.
Oil seed rape/canola is famous for crystallising quickly etc.....
If in doubt, immerse it in a sink of hot water, when the water goes cold, fill it up again and let that cool too. You should start to see the crystals dissolving, or at least getting smaller.....
And the reason for warming it like that is to prevent heating damage to the honey and driving off the aromatics and other VOC's that give the honey its varietal signature.......