No, this is coming from the SDMB. Earlier versions of Tapatalk automatically inserted a call to a Javascript function in your style sheet that pops up that window. It only gets called when it detects you’re on a mobile device and not logged in, I believe.
The remedy is to update Tapatalk to the latest version and then remove that old line from the default style (just search in templates for tapatalkdetect.js in the AdminCP). I believe the new version still has some sort of “hey, do you want to use Tapatalk??” message, but I think it’s easier to disable / ignore.