If a traveler prays behind a resident, does he complete the prayer or shorten it?

The questioner:
May Allah reward you, our Shaykh. This is my brother Muhsan from al-Ta'if. Please, go ahead. Peace be upon you.

The Shaykh:
And upon you be peace. How are you, Shaykh? May Allah reward you with good, may Allah keep you safe. We came down from al-Ta'if to Jeddah with my brother, and we caught up with the Zuhr prayer. The imam was in the second rak'ah, so approximately two rak'ahs were missed. My brother said to me after the imam finished, "I will complete the prayer." Which is better, completing the prayer and following the imam, or finishing with two rak'ahs? I finished. No, no. If one prays behind an imam who completes the prayer, it is obligatory for him to complete it and not shorten it behind the imam who completes it. If he prayed...

The questioner:
Yes, but my brother told me, "No, I am a traveler, so I finished immediately after completing two rak'ahs."

The Shaykh:
Yes, he must repeat the prayer. May Allah grant you well-being, because he made a mistake in this. His ruling is the ruling of the imam.