The numbers actually aren't floors, they're sections of the building code. 1 is nonflammable materials like concrete and 5 is most flammable but cheapest. (Pretty sure everyone thinks it means # floors though.)
4 is mass timber, which is a newer very promising material. The article mentions the airport used it, but you can build towers from it quickly, safely, and less chance of hearing your neighbors through the wall.
Oh, that makes sense. Ya, 5 over 1 makes sense in that context. They just happened to be height/floor limited as well compared to a pure concrete/steel construction.
4 is mass timber, which is a newer very promising material. The article mentions the airport used it, but you can build towers from it quickly, safely, and less chance of hearing your neighbors through the wall.
https://timberlab.com/projects/heartwood