My first thought was perhaps this could be done using 2.4 for one and 5ghz for the other, but while I was trying to find an example of configuring the radios independently, I came across DD-Wrt "Repeater Bridge" mode [1] so I don't see why that wouldn't be what the Pixel is doing.
[1] https://wiki.dd-wrt.com/wiki/index.php/Repeater_Bridge