I think Harold may have nailed it as far as the photo is concerned. But, that does little for you when the client hands it to you and asks when he can have it.
The thread on How Is This Door Made? is applicable to your questioning many ways.
Ladder cores and T+G faces allow for a small gap between the two pieces of solid wood - .030" or so - down in the bottom of the v-joints. If they expand (most likely in an exterior door), they will close a little or even mash each other in the "crush zone" between half "V's".
I see this as a veneered, modified hollow core door. 1/16" veneer faces, with a 1/16" cross band underneath. Pressed onto 1/4" MDF or flat, no void ply. Then the core, and the exact same on the other side.
This is then lightly pressed onto an egg crate at 1-3/4" thick (for 2-1/4" finished door) with rigid foam in all the voids. Have your solid matching wood edge bands, hinge block and latch blocks located in the egg crate. Turn down the vacuum pressure as you do not what the faces to bow into the voids from the evacuation of air. The foam and egg crate must be the exact same thickness.
The egg crate can be 1/2 x 1-3/4" pieces machined, not ripped, with dadoed at 15/16" deep so things do not bottom out and prevent flatness. 8x8 voids are good, smaller if you have the patience, larger if you like to gamble. Theory says if the foam and crate are exact, there can be no telegraphing of the egg crate to the face. But, if you notice it on a finished door, you are going to sweat.
You can do without the egg crate and use a ladder core, but I think the weight will go up significantly.
We just shipped a 2-1/4" x 60" x 116" Walnut door with a ladder core that weighed in at 325 lbs.
The hardest part is to get this door so you can "start flat, stay flat" (We chant this 30 times to start every day...). We have solid, leveled benches and blocks of uniform sizes so we know that as we assemble a conventional stile and rail door, that it is absolutely flat - and will stay flat. The joinery also helps this. But the type of door that gets its strength from all it parts will conform to a twisted or wavy vacuum surface or bench. You will need to take extreme measures to insure flatness of the door as it is clamped together. Even preliminary pressings of the faces will benefit from flatness. We stretch taut strings from corner to corner and compare the center to insure flatness from corner to corner. The rest is determined with straight edges and eyeballs.