A brilliant 30-yard shot from Sam Mantom had secured the visitors an equaliser following David Mooney's goal just before the interval for Orient, but Moses Odubajo popped up with a last-gasp winner to give O's boss Russell Slade cause for celebration.
Smith, who spent 10 years at the east London club as player, youth manager and assistant manager, said: "It's very frustrating because we should have gone in three or four up," he said. "We had the chances but we didn't take them.
"For me, to come away from this game with nothing is a travesty because I thought that we were the better team throughout the game and we were the aggressors coming away from home. I think they were very fortunate to end up with the points.
"We have been very consistent in terms of our recent performances and despite the result, we showed that again and played some really good stuff.
"We've opened them up and created chances and the game could have been out of sight at half-time.
"But it wasn't and that's what happens. One lapse of concentration allows them to score a winner, but we weren't really extended throughout the game and their keeper's made some great saves. It's just been one of those games."
- Sports & Recreation
- David Mooney
- Russell Slade