Interesting that it can only count iOS devices considering Apple is more privacy focused. What's the secret sauce that prevents Android phones being counted in the same way?

I would have thought Android's constant Wi-Fi scanning that Google uses for improving their indoor location services would be an easy give away.

Android does the same MAC rotation that Apple does, both on WiFi and Bluetooth. Working with IoT sniffing solutions at home, I've found it's reasonably easy to detect when a single MAC is randomly changed: it'll be broadcasting its presence, suddenly go dark, and then another mac with same first 3 bytes starts broadcasting with a very similar RSSI. This works with BLE adverts pretty well and allows me to filter out MAC noise from household devices while I'm trying to sniff something on my bench.

I'd assume it's because it's easier to look for an Apple MAC prefix than trying to figure out if some other device is a phone or not.

But with MAC randomization (both wifi and Bluetooth), I'm not sure what they are doing here that would effectively sort iPhones from other devices doing the same.

None of the developers ever saw one, or they firmly believe focusing on iOS makes the product more 'luxe'