It was funny when I got the update. I checked manually upon arriving home and getting on the Wifi in my garage and it said I was up to date. Then about an hour or two later I got a notification on my phone that I had a software update available. So the automatic checks seem to be unrelated to the once per day limit for manual checks.
Also, I've noticed that Tesla usually pushes firmware updates to my car on the same day as iOS updates. I'd think that was just an odd coincidence, but aside from once or twice when I got an update from a manual check, my last 5 or 6 firmware updates showed up automatically the same day as an iOS update.