I'm guessing them mean in terms of anything likely to actually unseat IE. Netscape->Mozilla->Firefox had been around years and were still only minor players ~20% market share. Chrome on the other hand saw nearly instant hockey-stick growth. I remember I switched almost instantly after a quick try and everything was so much faster.

There was Opera, as well.

But with all of these, you constantly ran into IE-only websites. Which got away with it because most people were running IE.

And that's why people are saying that Chrome is the new IE - because we're seeing that history repeating, with websites written only for and tested only on Chrome and Safari (and I doubt Safari would be anywhere if it weren't effectively forced onto iOS users).