engineerfag here…
concrete can and does deform elastically, but it's not talked about often. it's not the deformation that is so disturbing here but rather the fact that it being discussed at all.
everything solid has an elastic strain window but it's different depending whether in compression or tension, though bending moments create both.
so yes, but I don't know how much the ancient Roman's where contending with or factoring in if any at all. they may have kept everything in compression as one would without rebar or other reinforcement. still, the concrete objects in question need to be very large where any noticable elastic deformation is "safe"
Also, i've read the dam is not anchored to the bedrock, which falls under the tempting God with an "immovable object."
doesnt' seem to bode well, but it could last a couple lifetimes as far as I know