Having fallen behind to Johan Elmander's strike midway through the second half, Albion equalised when Peter Odemwingie flighted a wonderful cross for James Morrison, who headed home with 12 minutes of normal time remaining.
Coyle described the lively 1-1 draw as a "terrific advert for the Barclays Premier League" but felt that Odemwingie had been in an offside position when he received the ball before sending it in for Morrison.
"The disappointment for me is that with the goal that they scored, Odemwingie is clearly offside in the middle of the park when the ball is played through," Coyle said.
"Whether the assistant referee felt that another player with him was going to pick the ball up, I don't know.
"But he has allowed play to go, Odemwingie picked the ball up and although, I have to say, he showed tremendous quality in cutting back and sending a pinpoint cross in, we paid a heavy price for a decision that should have been stopped at source."
Baggies manager Roberto Di Matteo said he would have to watch a replay of Morrison's goal before he could comment on whether Odemwingie was offside, but was happy to come away from the contest with a point.
The Italian admitted his team - who created a major upset in their previous game by winning 3-2 at Arsenal - had struggled to find top gear and paid tribute to the visitors' performance.
"We were not at our best but considering that, I'll take a point against Bolton," Di Matteo said.
"The Premier League is a very tough league and some weekends there are some crazy results and surprises, other weekends there aren't.
"They (Bolton) were good and it was difficult. They work hard and never let you have time on the ball. Considering that some of our players were not in the best form, we still came back from 1-0 down and could have won it at the end - although I don't think we deserved to, to be honest."
Source: PA