You are correct that there would be a very short disconnect if the Roku was constantly searching for the strongest WAP. However, I believe what he was referring to was if the connected WAP went offline, most devices will search for another recognized access point and connect automatically. With a Roku, wireless connectivity to any access point other than the last used requires manual intervention. I have several WAPs in my home as well, but most of them use the same SSID, so my devices just connect to the strongest one depending on location.
Nvidia Shield, Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.