They aren’t one piece. See the dark seams? https://www.everythingkitchens.com/totally-bamboo-all-natura...

These are strips glued together aka laminated. The binder is not PVA (which is water soluble and not suitable for the task), it’s most commonly a formaldehyde resin such as phenol- , urea- or melamine urea formaldehyde

That’s plain bambu, the dark areas are the nodes/rings in the plant.

I don’t build cutting boards myself, but have never heard of using anything but food-safe PVA glue. Those resins are used for laminating plywood etc, probably not even legal to use in kitchen utensils, at least in the EU.