Despite scoring three tries in the final 10 minutes, the Exiles slumped to a 44-24 loss at Sandy Park on Saturday afternoon.
The result has seen London Irish slip down to eighth place in the table after six matches.
"Fair play to Exeter because they are a very good team and they played the conditions brilliantly," Smith told BBC Sport. "They have an outstanding defence and we weren't at the office in the first half defensively - that is disappointing.
"It was a disappointing changing room after the game. The captain is unhappy and I'm unhappy, but we will have to look at the tape of the game."
London Irish start their European Challenge Cup campaign next Sunday when they host Italian side Rovigo.