Flow's implementation of tooltips is not only different from desktop's watchlist notification but also broken on mobile (they cannot be read, being clipped off screen)
Mobile uses a toast module to deliver all notifications so this is a big inconsistency with the rest of the application.
Flow should be helping drive standardisation around this.
Take a look at
mw.notify( 'foo' ) in desktop
mw.mobileFrontend.require( 'toast' ).show( 'foo' )