The basement battle at the Kassam Stadium was ruined as a contest by the 10th-minute sending-off of Hala'ufia for a dangerous tip tackle.
Smith said: "I thought it was a perfectly executed tackle. The referee made a big call as he was not 100 per cent sure of the decision as he had to check with his touch judge.
"I would like to see the rugby league system brought in where a tackle like that goes on report and is assessed afterwards."
Lyn Jones, his Welsh counterpart, said: "There was no malice in the tackle but the referee's hands are tied. It was very similar to the Sam Warburton incident in the World Cup when the Welsh captain was sent off."
Despite the loss of Hala'ufia and a subsequent yellow card for Matt Garvey, the Irish battled to the end and nearly pulled off an unlikely win.
"It was an unbelievably gutsy effort and could have been a gutsy victory," Smith added. "We are not happy but we have salvaged a bonus point.
"I'm not going to blame the referee for our loss as we weren't precise enough and we lost 15 points with missed kicks."
The match was a dreadful spectacle with neither side having any attacking invention to break down the opposition's defence and it was left to Gordon Ross to secure victory for his side with five penalty goals.
It was a crucial win for the Welsh as they continued to battle for Premiership survival.
"All wins are good wins but our ill-discipline cost us dearly," Jones said. "We were good value for the win and they scrapped hard for their bonus point.
"Our defensive structure was very good and we are targeting six wins for survival, so with four wins so far we are well on target."
Welsh lost Hudson Tonga'uiha in the sixth minute, with Jones revealing after the game: "Hudson has gone to hospital to have his shoulder put back in. He is a big loss for us as he is a key player."
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