The new document at Pre-download with Local Firmware Fetch - Cisco Meraki Documentation could do with a couple of corrections in the first paragraph:
Introduced in MR 32.1.2, Pre-download with Local Firmware Fetch allows an AP, to download firmware from Dashboard and distribute image to other APs over the LAN, cutting down on image download times and high load on the cloud backend infrastructure. During the upgrade process, APs within a network are divided into groups. Within these groups, APs are randomly selected to be servers. Elected server APs will download the relevant image from the Dashboard. Remaining APs that are apart of the local area network can then retrieve the image from server APs.
If my answer solves your problem please click Accept as Solution so others can benefit from it.