I'm surprised DDG can donate so much money to open source. They must be doing well? Or is this money they've helped raise from their users? $225,000! That's a lot of money.
Additionally the donation itself got a vast amount of coverage in the relevant communities, including HN, so the expenditure is offset against advertising for user acquisition they didn't need to do. It probably also strengthened their core community, making their users more sticky. The donation also went to some of the infrastructure they use anyway.
After 6 years, Google was doing 200m searches a day.
Google now does something like 4 billion a day. So duckduckgo, after 8 years of growth, has captured about 0.3% of the search market. At that sort of rate, it'll take decades to get any meaningful share, and that's assuming Google stand still, which they won't.
Seems to be a fairly good deal. I try to convince the bosses where I work to do something like this and they just roll their eyes at me.