Salah went down in the penalty box under the challenge of Arthur Masuaku shortly before halftime when the Hammers were leading 1-0, and the Egyptian duly picked himself up to tuck home the resulting spot kick.
Substitute Diogo Jota scored a late winner for Jurgen Klopp’s men to leave West Ham winless in their last three Premier League games.
"I’m amazed that a penalty was given in the first half. I can’t believe that we’re allowing those sorts of penalties to be awarded," Moyes told Sky Sports after the game.
"We weren’t clinical enough at times. We missed a couple of really good opportunities to get another goal.
"In a lot of games we feel we can challenge. We go into many games thinking we’ve got a chance. I wouldn’t say we were unlucky today, but I’m really disappointed when we were 1-0 up that the penalty was given."
Speaking to BBC Match of the Day about the penalty, Moyes added: "It’s not the sort of football I want to be involved in. I think our player stops and throws his arms up because he’s so disappointed about the dive.
"I’m just disappointed they didn’t turn the decision around. Maybe in the second half the decision [Diogo Jota’s disallowed goal] went for us, but the first-half one didn’t."
West Ham have dropped to 13th on the table and host Fulham in their next game.
