For background, here are some of the basics. There are two “Bluetooths”: Classic and Low Energy (LE). The former is the streaming standard that everyone knows through wireless headsets and speakers, while the latter is basically what every modern peripheral device or hardware accessory, such as a smartwatch, uses to transmit data.
LE is also called Bluetooth Smart. LE is bursty and lower power (though not necessarily inherently more efficient), and was designed to enable devices running on coin cell batteries. You can do crazy things like stream video over it, though, if you so desire. (Don't do that.)
I’ve been vaguely keeping track of progress on BLE audio for a few years. I knew that the Bluetooth SIG was working on an LE audio standard, but am amazed that Apple secretly deployed its own in 2015. But it’s not magic, and is still based on LE. “Configuring the HAs is performed through LE services & characteristics, but the audio streaming channel is secret sauce.”
Bluetooth LEA, as Apple calls it, is not used by the AirPods. I’m not sure why, but it may simply be because LEA’s quality is still inferior to Classic audio streaming. Streaming audio is inherently difficult because of LE’s lower duty cycle, which is what makes LE more efficient in general.
Pairing is the same as for the AirPods, using standard LE protocols, though there may be specific codec features that Apple depends on. To emphasize, this is all still built on top of standard Bluetooth. And I believe the SIG is working on a similar pairing UX feature. (Keep in mind that pairing is not required with LE as it is with Classic. Otherwise, say, Bluetooth beacons wouldn’t exist.)
I frequently see people complaining that “Bluetooth sucks” or “Bluetooth is always supposed to get better next year.” Before they were announced, for some reason people even wondered if Apple was going to replace “Bluetooth” for its AirPods. The problem is that people are almost always thinking of the wrong Bluetooth.
I won’t fully explain it here, but basically Classic and LE are different radios. To oversimplify: you can think of Bluetooth 4.0 and later as a completely different spec than 3.0 and earlier. For example, Bluetooth 5 has absolutely nothing to do with the Bluetooth that people normally think of (Classic).
* Thanks to Brendan Sharks for suggesting a correction to the article title.