I see this @arstechnica article is trending. It's inaccurate in a problematic way, though.
"Port 5353/UDP" is not just some "field" - it's a whole another service discovery protocol by Multicast DNS. In this case, your iPhone looking for AirPlay targets after making a new network connection.
The reason this matters is that Wifi privacy was presented as a way to hide your device identity from pass-by Wifi networks you didn't even connect to, and it does that. Revealing your device id after you've connected isn't great, but easy to mitigate: just don't connect your devices to random public Wifis. There are much worse problems you're exposing yourself to if you do that.