The Chairboys' captain Lewis was given his marching orders in the 34th minute for what referee Gavin Ward regarded as a dangerous challenge - a decision that looked harsh.
With the visitors still reeling, Luke Moore headed in the only goal of the game to give Wimbledon their first win of the new season.
Ardley said: "I can see why he sent him off because it was a very high challenge and a late challenge, but if I was Gareth I'd probably be disappointed.
"At that time I don't think it had been a particularly nasty game and I would have been disappointed had it happened to us but I can see why he's given it at the same time.
"We made some points to the players on Thursday after the Millwall game about our tempo of play and I thought in the first half the tempo of our play was excellent.
"We caused them a lot of problems and there was a lot more pace about us and even when it was 11 v 11 I thought we were the better team.
"Obviously what was quite important was that when they did go down to 10 men we got a goal quite quickly and they didn't get a chance to sit back."