The visitor observed that there was already enough space. The Prophet’s ﷺ gesture shows that courtesy is not merely a response to an urgent need; a small movement can welcome someone and affirm their dignity.
For example, shift a little to welcome a fellow learner, leave comfortable room in a mosque, or offer suitable seating to an elder.
These manners should be practiced willingly. Pushing others aside, taking away another person’s rightful place, or causing disruption would contradict the purpose of courtesy.