Southampton have enjoyed another impressive season in England's top flight.
Long opened the scoring at Villa Park and Koeman spoke about the marksman's regret at not adding to his tally, as reported by the Irish Independent.
"He apologised after the game because he wasn't scoring more goals that one," Koeman said. "It's a good mentality because he had some good possibilities to score."
Koeman spoke in the week about his target of four wins out of the Saints' remaining four games, and that a European spot is not out of the question.
He has even more reason to be bullish now, with Liverpool dropping points and West Ham United not playing until next weekend.
The south coast club currently sit in eighth position in the Premier League, just one point behind Liverpool and two behind West Ham, although they have played a game more than both sides. Koeman, however, believes they are well in the race.
"What you like, at the end of the season, is to play for something, that is always better than when the season is over," he said. "We are winning again and putting the pressure on them. That's what we like to do and we have to do it next week."
He also pointed to the fact that Liverpool's European commitments could have an adverse effect on their Premier League form and something his Saints side can take advantage of in their quest to usurp the Merseysiders:
"Liverpool have a tough schedule with the Europa League and that's always difficult to keep the momentum in the Premier League. That's good because we are close but we need more wins, we know."
Next up for the Saints is a visit from Champions League semi-finalists Manchester City.