Description of Henyey tracks on wikipedia incorrect?
The wording provides a contrast with the Hayashi track phase that immediately precedes it, where the luminosity decreases by orders of magnitude with little change in effective temperature.

You are correct though, the Henyey track for low-mass stars is not horizontal in the HR diagram, however it is a critical point that the luminosity does not change very much (less than a factor of 3) as the effective temperature increases, since it implies that the star slowly shrinks, and by the virial theorem, the core temperature gradually rises and is ultimately able to sustain nuclear fusion.