On Wednesday, the British team announced that their Belgian rookie driver will stay with McLaren in 2018, notwithstanding his often tough opening campaign alongside Fernando Alonso.
"To me it was not a surprise because I had a multi-year contract already," Vandoorne told Sporza news agency.
"But it's always nice to know that the team bosses have confidence in my abilities."
Vandoorne also told Belga news agency: "Getting confirmation is always good because now I have 100% confidence that I will be in Formula 1 next year.
"That gives me psychological rest for the remainder of the season - not that it really played on my mind. But as I said, getting confirmation is always nice."
In the official press release, McLaren had described Vandoorne as a future world champion, and Vandoorne said that was nice to hear.
"Hopefully that will be true one day," he said at a sponsor event ahead of his home grand prix at Spa Francorchamps.
"At the moment the results are not there but all the ingredients are there to be successful in the future. Hopefully I can take a step forward next season.
"After a difficult start we have made a lot of progress and the last races in particular were positive for me, especially compared to Alonso."
Vandoorne admits that the start of his F1 career was especially difficult.
"Everyone knows our situation," he said. "But since the beginning of the year it has been improving and hopefully that will continue in the coming weeks and months.
"As for whether I can take a real step next season, we will have to wait until the [winter] tests in Barcelona."
More immediately, Vandoorne will have his first home race in Belgium this weekend, but he is not expecting a competitive outing at Spa Francorchamps.
"I'm obviously looking forward to it," he said, "but for our team, Spa is not a good circuit."
Vandoorne has picked up one point so far this season.