It all goes back to the explainer he published in November which — in short — says that if a device or charger users Qualcomm’s Quick-Charge 2.0 or 3.0 technology, it is by its very nature, not compliant with true Type C. In fact, he says that USB Type C specifications “forbids” having QC and Type C coexisting. Since both the HTC 10 and LG G5 support QC 3.0, it follows that neither of those phones are compliant with Type C, despite having the Type C shaped connector.
The Type-C spec specifically forbids proprietary charging methods that try to change Vbus beyond 5V.
The longer explanation to this is that Qualcomm’s QC 2.0 and 3.0 use a variable voltage method to get more power over the same USB A to Micro USB cable. He doesn’t argue that Type C is faster than either QC 2.0 or QC 3.0 at charging, in fact, it’s probably not. The Motorola Turbo Charger which shipped with the Nexus 6 (for example) can output up to 18W charging over a Micro USB cable, which is more than the 15W output offered by the 3A Type C chargers.
The differentiator is that because Quick-Charge is a proprietary Qualcomm tech, it takes over the USB data lines, and means you can’t use a data connection (to your PC for example) at the same time as using Quick-Charge. USB Type-C doesn’t have that restriction.
This section of the Type-C specification 4.8.2 calls out chargers and devices that want to use a proprietary charging method and restricts them specifically from modifying Vbus (which is what QC does to get to 9V and 12V), and from altering roles from source to sink.
In short, your HTC 10 and LG G5 might be able to charge really fast, and have a fancy new reversible connector, but they’re technically not Type C compliant. At the very least, the chargers that ship in the boxes aren’t compliant, according to a Google engineer.