Van Buyten completed his switch to The Premiership on Saturday to link up with City for the rest of the season.
The Belgium international admits he is relishing the chance to test himself in The Premiership, with the prospect of a permanent deal in the pipeline.
But the centre half says he was annoyed to leave Stade Velodrome and insists it was Marseille's decision to sanction the swap deal.
"We had to take a quick decision," van Buyten told L'Equipe.
"Olympique Marseille received a very interesting proposition from Manchester City and they wanted me to leave.
"I am not used to leaving like that, in the middle of the season.
"I am a little disappointed to leave Marseille, an extraordinary club, which allowed to me to enjoy great things, with unique fans.
"I am quite annoyed but I don't want to talk about that.
"Now, I am in England and I am eager to see if my game can adapt to the Premier League characteristics."
French stopper Sommeil headed to Marseille in part-exchange after just 12 months in The Premiership, although City boss Kevin Keegan has not ruled the 29-year-old out of his plans permanently.
Sommeil concedes he had no yearning to leave The City of Manchester Stadium but was not going to snub Marseille once the opportunity arose.
"There was contact at the start of the week between the two clubs but everything accelerated on Friday," commented Sommeil.
"I don't know really which of the two clubs were leading the exchange but Manchester City wondered if I would agree to join Marseille. I replied in the affirmative.
"I did not have the desire to leave Manchester City but when a club such as Marseille call for you, you cannot say no.
"L'OM are always at the top of the standings and I also knew they had followed my progress before. This time, I did not hesitate."
The central defender also acknowledges his time with City has proved to be a valuable learning curve for the remainder of his career.
He added: "For me, that will remain a good experience. I feel that I have learned a lot, notably on the approach to matches.
"Life in England is completely different. All that will serve me well for the continuation of my career."
