On Tuesday, the Milton Keynes-based team confirmed Vettel had agreed to a one-year extension through to the end of 2015.
Vettel has been a part of the team since 2009, claiming 29 victories, 39 pole positions, and winning three successive titles since 2010.
"It was more of a formality than anything else," Horner told the media.
"We have a long-term agreement with Sebastian, and it was just perfect timing for both sides to extend for another year."
Although the announcement was a surprise initially, the main question that has since been raised is why Vettel has signed for only one further year.
Horner believes Vettel putting pen to paper again is simply a sign of the trust the German is placing with the team.
"The details of the contract between the parties are always going to be confidential," added Horner.
"The fact he has signed this extension shows his commitment to Red Bull, and hopefully the relationship will go beyond 2015, which is already some way into the future.
"He's been part of the Red Bull family, since starting out as a junior, for more than 12 years now, so he's grown up with Red Bull.
"He's achieved all 29 victories in cars designed by Adrian (Newey, chief technical officer), and he is still growing and developing as a driver.
"He enjoys the environment he is working in, we enjoy having him and working with him. It's a relationship that works."