I don't think flexbox really started being used until 2013 at the earliest, the comment I replied to was complaining about 2022 and a flexbox bug in IE. This 2012 thing doesn't seem to relate at all to the subject.
on edit: I know it was in WD in 2009 but I'm pretty sure it was around 2013 that people started playing with it. I think it started being popular in 2014-2015.
My comment was more about the prevalence of IE in general, not flexbox specific. There were tons of IE quirks that had to be dealt with.