So my best guesses are:
1) $30M is basically a BS, "maybe they can get it in some crazy situation number"
2) $30M number is not real at all
3) They had some technology that was patented, hard to build, and was perceived to be super valuable to Yahoo but not obvious from the app itself
4) Something about having this "wiz kid" was really important to Yahoo's image
And it was definitely not:
-the product (being shut down)
-much of the team (only 3 are going with)
The lessons from (1) and (2) would be don't believe everything you hear. The lessons from (3) and (4) are that having great corp dev resources (VCs, advisors, etc) are worth a whole lot.