The Saints were expected to struggle in Premier League this year after the mass exodus of players in the summer but against expectations, Koeman has led the club to the possibility of European football next term.
Dutch tactician Koeman, who replaced Mauricio Pochettino last summer, credited the club's youth academy for helping the senior side deal with the loss of such players as Adam Lallana, Rickie Lambert, Luke Shaw, Dejan Lovren and Calum Chambers.
He said: "I'm not surprised because it is a very well organised club, with a strong club structure and has a very good academy.
"It is a famous club because good players came out of their academy, talented players, and become great.
"Gareth Bale is the case. Now he is a star at Real Madrid and comes from [the youth system of] Southampton. Theo Walcott and Alex Oxlade-Chamberlain [who are at] Arsenal, also grew up here. We are known for this.
"Having a good structure is everything. In England there are other examples where money talks but here the model is more sustainable.
"It gives us the chance to play well, gives opportunity to the academy. It has continued the good work Mauricio Pochettino did last year.
"It was not easy, because many players were sold in the summer. But with work, a team that is almost new is ready to fight to get into the Europa League.
"A lot was achieved in transfers to invest in other good players. The scouting club and have done a great job to put together a good team. It is a very big chance for a humble club and a superior goal that not everyone expected of us."