Yes, but there is more.
Brown characterizes his subterranean oceans as supercritical water. Supercritical fluids have some unusual properties, but an aspect of the basic idea is quite accessible. If you heat liquid water, its density will decrease, as is readily seen in an old style thermometer. Steam is a compressible gas, and as you increase the pressure, its density will increase. Eventually, you add enough heat and pressure, and the density of steam and of liquid water become identical. Gas and liquid become indistinguishable, and there can be no interface. This is a forth state of matter, and fluid supercriticallity is not that rare in process engineering.
If liquid water could not provide support for Earth’s crust, the situation is so much worse with supercritical water.
One, liquid water is relatively incompressible compared to supercritical water. which is still approximated by the idea gas law. That means supercritical water provides essentially no mechanical support countering gravity, for the vast overburden between any pillars.
Two, the viscosity of supercritical water is an order of magnitude less than liquid water. It would wedge between microscopic crystals, and any minute fissure or fault would be like a freeway. There could be no rock or mineral which would be impervious to the progressive ingression of supercritical water, even before tidal deformations. Structural loss of integrity of the crust would probably happen before the serpent was done with Eve.
That hydroplate theory gained traction with even a fringe of YEC is a demonstration of just how sciency sounding language can sadly bamboozle a trusting audience.