The "glass is a liquid" thing is a myth. The reason why old windows tended to be thicker at the bottom (which is usually the cited reason for this myth) is because windowpane making techniques weren't very good and so they would always have one thicker side. The builders would naturally install the pane with that side on the bottom because it was more stable. Glass doesn't "flow" over time, it's a solid ~~crystalline~~ amorphous material.

They bounce a laser off the glass and can hear what's happening in the room by capturing the vibrations of the glass. I seem to remember the US embassy was caught spying on the Canadian Prime Minister using this technique.

Yes that's possible and it has some years but there's some conditions. The glass needs to have a sticker onto it for the trick AFAIK is to reflect a laser or infrared light onto it and track the less than milimétric vibrations of it and depending on where is the sticker and how big is the window it affects the quality of the recording. Given this wifi trick I think it would have to do with signals not passing through water clearly or some thing on the likes and more over it should need some specific equipment to pull out the trick, I don't imagine you could just hack a router and patch surveillance in the firmware.