I'm the guy from RethinkDB who found and hired Jeroen!
I will say it's pretty rare, but when searching for a very particular skill set "Who wants to be hired" can totally work for finding new to mid-level devs.
Well, at the time something in the list of "C++ (Boost, STL), Python, SQL (PostgreSQL, SQLite), git" caught his eye.
Since it was RethinkDB I suspect the combination of C++ (which RethinkDB is written in), Python (one of the 4 languages for which there are/were "official" libraries), experience with 2 different DBMSs and an interest in "a challenge as a backend enginer to further hone my C++ skills" were probably all factors.