I recently purchased the Beats Studio 3’s and starting I believe with IOS 10 and above, Beats headphones with either the W1 (Solo 3 and Studio 3) or H1 (Solo Pros), are now updated automatically when connected to power and are connected to an iPhone or iPad. It’s the same process in how AirPods are updated...AirPods in their case, connected to power and when opened, they connect to a paired iPhone/iPad and during that process of connecting, any updates are sent to the AirPods.
if you turn off your headphones, plug them in then unlock your phone...and then turn on your headphones, you will see the connected pop up with your headphones...That’s when the firmware is checked and then updated if needed...
Probably explains why you got the update without using the updater app...I actually contacted beats support and they confirmed when used with an iPhone/iPad, this is how their headphones are updated now. They keep the update app around for older non W1/H1 headphones and for people using android...
It’s mentioned briefly here, scroll down to the update section...
https://www.beatsbydre.com/support/how-to/set-up-and-use-solo3-wireless
As to what was updated, it probably was audio sharing...
https://www.theverge.com/2019/9/20/20876213/beats-apple-audio-sharing-airpods-ios-13
