It seems like a highly questionable decision to do what the pilot did. This was a busy highway and the possibility of a collision with a road vehicle was high.
If one looks at the vicinity of the airfield in an online mapping application it is clear that this is not a densely populated area, a good description might be suburbia.
The garden centre mentioned in the article, Floralies Jouvence is annotated in the image above. The aircraft made a force landing in the vicinity of this business and it is clear that there are many surrounding fields which could have been used rather than the highway.
The other remarkable thing is that the article states "Around 10:30 a.m. Thursday, the pilot of the Piper Cherokee aircraft called the Quebec City fire department asking for permission to land on the highway just a few kilometres south of the Jean-Lesage International Airport." - So the pilot had time to make a phone call (presumably) and request permission to land on the highway. The indication being that there was an appreciable period of time between the occurrence of the mechanical failure and the landing, time which would perhaps have been better spent on a planned approach into one of the numerous surrounding fields.
Whilst landing on a road is tempting, roads come with many stationary obstacles such as road furniture and electricity/telecomms wires. That is even before the vehicular traffic is concerned.