The skeletal horse spawned by a lightning strike has 53 health, far more than any other naturally-occurring horse.

This seems to be the interaction of two underlying bugs:

• When the "set random horse stats" method isn't called, the horse defaults to 53 health. 23 would be more in line with the defaults for movement speed and jump strength.
• When lightning spawns a skeleton trap horse, it doesn't call the "set random horse stats" method.

Somewhat related (i.e. the obvious fix for the above would result in this for the lightning-spawned horse too) is that the spawning of the three additional horses when the trap is triggered generates their stats as if for a normal horse or donkey, rather than for a skeletal horse. The effect of this is that these horses get randomized health (15–30) and movement speed (0.1125–0.3375) rather than the static values (15 and 0.2) that the "set random horse stats" code seems to intend. The code to do it right seems to already exist, you just need to pass a new vu.a(vw.e, 0) instead of null to the "set random horse stats" method.