Yes & No. It is not sterile, but essentially sterile.
The only water that interacts with peat prior to harvest is rain water. Rain water is sterile by nature.
Bogs are not horticultural land, so the typical pest and disease associated with mono-culture growing are not present.
When peat it extracted it is done by vacuum then stacked/stored on the bog to avoid any pest or weed seeds to enter it.
After that it is sealed in plastic. Unless that plastic is broken or opened there is no way for disease or pest to enter it.
Peat does have natural beneficial microbes that help keep pest/disease from growing in it. If you were to sterilize it you would kill these microbes.
Is Peat Sterile?