"It surprised me. In fact I think it has come as a surprise to everyone," he said. "It is not often a player leaves one big club to go to another like Arsenal or Liverpool. It does not tend to happen.
"But Mikael did not play much last year and I think he just wanted to go somewhere where he would, so in that sense I am happy for him."
Vidic has grown close to the former France international during his own two-and-a-half year stint.
And, while it was obvious Silvestre's first-team chances at United were strictly limited, Vidic believes the 31-year-old is still a class act.
"He has been here a long time and he still deserves to play at the highest level," said the Serbian.
"Mikael has given so much to this club. I am just surprised he is going to Arsenal. But he has made the choice."