Incorrect time zone for Tadoussac (and maybe more)

We just received some feedback on our app from someone who lives in Tadoussac, Quebec. They said that their time is off by two hours. I looked into it and found that the time zone is incorrect for their city.

I found the problem by making a geolookup request for the coordinates of Tadoussac: 48.1431, -69.7192. The reported time zone (MDT) is not the correct time zone (EDT). Is there a reason why this shows the incorrect time zone?

Thanks,
Tim