I don't remember the details, but on a previous article on wooden skyscapers, it was explained how the engineering of the wood, which is also required for the necessary structural strength, made it very dense and practically incombustible. Fire proofing is an inherent quality, not something that's applied and thus could be done poorly.

IIRC.

The wood is all treated and sealed, so flammability is largely mitigated.

Even with steel, the actual frame of the building is surrounded by firewalls, fire resistant insulation and various suppression systems.