From the chart it seems like the sales were much more drastically affected by external promotion (being featured by Apple, mentioned on TUAW, and cross promoted from the other app) than any search algorithm changes.

In my opinion, considering how many timer apps there are in the App Store already, making $5k in a little over a month is a pretty good result. That's a nice little passive income stream of $127/day for an app he probably doesn't have to put that much more work into (although I don't think those numbers will be sustainable).