I agree, Heartbleed is a big miss. Before reading the article, the two that came to mind were Y2K and Heartbleed. Notwithstanding all the recent security breeches (e.g., Ashley Madison, Sony) that could be attributed to "bugs".
If you're limiting it to the "The 5 Most Infamous Software Bugs in History," Heartbleed is definitely out. It just happened to be recent, so it has an outsized place in people's minds. Including it would sort of be like those foolish "Top 100 bands of all time" lists that have the Beatles at #1, followed by 85 bands from the last 15 years.
As others have noted, the big miss is the Therac-25 bug, which is pretty commonly taught in Software Engineering/Computer Science classes the example of how intangible software can kill people.
