From the article:

"Of the 135 Space Shuttle launches, only one (STS-51F on 7/29/85) experienced an abort-inducing failure during ascent. In the case of 51F, they safely made a lower-than-planned orbit and carried out the mission. All of the other flights cleanly avoided the dubious honor of settling the RTLS bet."

All but one. Did the writer just forget about the Challenger mission, or did that one somehow count as "cleanly avoiding" an "abort-inducing failure"?

(Someone in the comments to the article has brought this up as well.)