The premise is flawed -- assumes they were climbing over a thunderstorm (and a relatively small one if it tops out in the low 30's -- others in the area reported up to 52,000 feet). Airlines frequently climb or descend to avoid turbulence, not just thunderstorms. If they knew the clouds ahead of them were at the same altitude as them, they may have initiated a climb to avoid the turbulence associated with the cloud layer.
Gotcha. Thanks very much.