Edit: I think it was https://www.chrisstucchio.com/blog/2013/hadoop_hatred.html, HN discussion https://news.ycombinator.com/item?id=6398650
But the idea wasn't that data was big as soon as it didn't fit in Excel anymore - Excel was a reductio ad absurdum. If it still fits in Excel, it's laughably far away from being "big". That was the idea.
Big data was about the problems you get when you need to join data together that you can't fit well in one database server, not even with the amounts of memory and disk space you can get these days. It was Google type problems, the stuff that map-reduce needed to be invented for. The kind of problem that most companies just don't have.
So the term mostly disappeared from job descriptions, "data science" became popular instead, and people keep using Excel because it is great.
(that blog post is from 2013 so it can't be the source of that quote from 2012. But please don't define big data in terms of Excel in a 2021 MSc thesis)