I'm very confused, can you clarify what makes this different from the gesture that highlights text?

Edit: it appears that "request desktop site" makes it fit the viewport, whereas using the mobile view it's I guess already fitting the viewport so it highlights the text. The strange thing is in the desktop view, if I pinch zoom after fitting the viewport and do it again, it zooms out, whereas the mobile view still highlights the text. Which kinda makes sense, since mobile view it's fairly likely that you zoomed in to highlight the text more accurately, though it's weird that it's so inconsistent.