ANTI-SKID is fitted to and operates independently for all 4 main wheels (axle pairs in alternate braking mode).
As I read the original post, Hydroplane protection (wheel has decelerated > 50 kts below ground speed) was only on wheel 1 & 3. Though, the OP called this function "Touchdown/Hydroplane protection" .. so I am not really sure what was meant.
Touchdown protection prevents the A/C landing with the brakes already applied, and only operates on 1 wheel on each axle.
In my simple mind, if you're on the brakes during landing you'd still blow tire 1 and 3 (if only 2 and 4 has touchdown protection).
I am sure there is a good explanation, and if you find something I'd be happy to learn. But so far this doesn't make much sense to me...