Pressboard products may have formaldehyde based glues. Dogging California is easy, but that stuff really isn't good for you. Remember the FEMA trailers? People were living for long periods in things designed and certified for occasional use. It's all about the outgassing of new materials, and the low-level of air exchange in the trailers. If you use new masonite, particle board or pressboard in a coop, and you don't paint it, you'll probably notice some odor for a while. Do you have enough airflow in your coop?
Anyway, the linked article is in reference to a municipality burning pallets. They're probably looking at thousands of pounds of biomass being processed by hourly laborers, not half-a-dozen carefully selected used pallets from a local warehouse.
If you want to use pallets to make a coop with (good looking coops, by the way!) and you're worried about contamination, try this:
1) select the best, cleanest looking pallets you can. The wood should be wood colored.
2) pressure wash them at the local carwash to blast any junk and bugs out of the grain and corners.
3) paint/stain with something to seal the grain. If pesticides or bleach got into the wood and didn't rinse all the way out, that should encapsulate it.
Instead of freaking out, use some sense.