Ports/devices with older connectors (USBA, mini-B, micro-B, B) aren't necessarily going to be able to (or supposed to be able to) handle a 3A current draw.
A device that supports USBC should handle current draws this high. But to do so, it must be able to determine if it is safe to draw this much current. That's only doable with a USBC->USBC connection as per spec. So a USBC-USBA cable (or any other USBC->something cable) should use a resistor identifying that the USB3 current draw spec should not be exceeded.
The cables he's reviewing misidentify as being capable of the full current load. This could cause damage to the device your USBC phone or laptop is being plugged into.
Benson has posted instructions if you want to test a cable yourself and you have a 2015 pixel: https://plus.google.com/+BensonLeung/posts/jGP5249NppF
The problem is that you'll need a sacrificial USB charger, and if you're lucky, you'll find out from the Pixel's diagnostics whether or not the cable is dodgy. If you're unlucky, you may also find out when the USB charger dies. In Benson's words, "Plug in the suspect USB cable and plug the other end into a DCP charging wall wart (preferably one you don't have any sort of sentimental attachment to)".
Also read all the way through to the end. There are instructions for how to do this without needing to put the Pixel into dev mode, which is useful for those of us who need to use the Pixel in its enterprise enrolled mode to access our corporate accounts. :-)
Sadly Apple have a variant of that floating around, resulting in confusion and devices that can do 500mah to anything, and 2400mah to Apple devices. Or anything if you fake them out via rigged cables etc, giving us the monstrosities called "charge only" cables.