Those little white bugs are wood mites!

I would bake your substrate at 225 in the oven for like 15-20 minutes. Obviously let it cool down when its done.

Also, use a light bleach solution to clean the cage. Make sure you get every nook and cranny. Although wood mites are not harmful to your snake, you don't want the cage to be infested with them.

If you can, order a can of Provent a Mite just in case they come back again or you get snake mites.