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.