Goals from Peter Odemwingie and Youssouf Mulumbu gave Albion victory and leave Villa downbeat after their recent four-game unbeaten run effectively ended their relegation fears.
McAllister said: "It was not necessarily an end of season performance.
"I just feel it was an opportunity to grasp three points away from home against a local rival.
"We got ourselves in front. The first goal was a poor goal to concede and an unneeded challenge, then we didn't defend the set-piece. Then when West Brom went down to 10 men it was a great chance for us.
"We stuck in a lot of offensive players with skill, pace and guile but we couldn't break down West Brom - and then we got done with a sucker punch.'
Source: PA
Source: PA