Any guest for whom the Extra Guest Fee has been applied — meaning the "Extra Guest Fee" toggle was enabled and a fee amount was set — is considered an extra guest. Since the toggle was on at the time of adding guests and a fee was defined, an extra guest fee was automatically applied as an upsell for each additional guest.
Note: If you didn’t want the Extra Guest Fee to be applied as an upsell, the "Extra Guest Fee" toggle should have been turned off when adding the guests