A BBC navigation bar component broke depending on the external monitor

RE this line of code at the bottom of the article:

  const isInvokedByMouse = event =>
  event.type === 'click' && (event.screenX !== 0 || event.screenY !== 0);

Why do you even have to check if screenX and screenY are non-zero (as opposed to just checking typeof event.screenX == "number")? Wouldn't that mean (and this is a wild edge-case) that if someone positioned their browser window so that the menu was in the top left corner (at position 0,0) the event handler would break again? Is this to block synthetic click events like (<div />).click()? Keyboard events don't have a screenX or screenY from what I remember as well.