Horn told The Times-Picayune that he was working out by himself in Mississippi when Thomas celebrated his 72-yard touchdown against the Los Angeles Rams.
"When I saw him bring out that cell phone, I teared up," the 46-year-old Horn said, via the newspaper. "That's something that some kids don't do, to pay homage to an old soul. For him to do it on a national stage took a lot of courage. I'm humbled."
Horn also said that he immediately purchased Thomas' No. 13 jersey after the touchdown.
A four-time Pro Bowl selection, Horn set franchise records during his seven seasons (2000-06) with the Saints. His 7,622 receiving yards trail only Marques Colston and Eric Martin.
"I'll always appreciate Saints fans for all they did for me," Horn said. "I will always love the city of New Orleans and when I come back there again I'm going to be wearing my Michael Thomas jersey."
Thomas said he watched Horn's celebration in 2003 via YouTube.
"I loved the celebration," the 25-year-old Thomas said. "I loved the swagger that he brought. I love how it got the crowd going. I definitely was thinking about it, but I'm happy I waited for that moment."
Thomas finished with 12 receptions and a franchise-best 211 yards for the Saints (7-1), who posted a 45-35 victory over the Rams (8-1).
The Saints' previous single-game receiving record was 205 yards, set by Wes Chandler in 1979.