Ever since Atlantis, I’ve noticed that Broadcom Drivers seem to come with the LiveUSB, through testing on my actual machines that do use them.
If you do an Online install they are in the Base-Devel + Common Packages category (I think that’s what it’s called), but are they installed onto your system on a post-offline install?
offline install will use the same image that you have on booting the ISO (Live Environment) so yes it has broadcom (broadcom-wl-dkms) but install process is detecting if drivers are need and if not they will get uninstalled.