The Baggies lost their first Premier League match after an unbeaten run of three games, leaving their boss lamenting their performance.
"I thought first half we were too passive in the game," he told Sky Sports News. "We didn't pass the ball as well as we do and we didn't create enough.
"We had one or two half-chances as Newcastle did. The goal came out of nowhere because the game was drifting towards a goalless first half and then we conceded the goal.
"The second half was good. We played with more intensity, got ourselves back in the game and then a wonder strike denied us any points."
West Brom are currently 12th in the league table with 15 points from 13 matches.