Large solid timber beams actually burn incredibly slowly: partly because they're so dense, and because wood is a good insulator. For a similar thickness beam, wood takes much longer to fail than steel when superheated. At 1100F, steel starts turning into spaghetti. But on wood, the layer of carbon created by the char becomes an insulating barrier that reduces heat on the non-charred side by up to 90%.

A bigger concern to me is the wood rotting from exposure to water or chemicals. Although reinforced concrete also "rots", but in different ways. Wood at least tends to sag before failing from rotting, unlike concrete.

I'm kind of surprised they don't utilize things like steel torsion boxes for the foundations instead of concrete, but perhaps there's cost considerations. They could do a lot of fancy things to extend the size of wooden buildings using steel if they don't mind losing those fire retardant properties.

Also, it should be mentioned that wood-based buildings can re-ignite after an initial fire, which doesn't happen with steel or concrete. While you may escape the fire and the fire gets put out, the structure may still not be safe. We may need new fire codes if these buildings become commonplace.