It's for networking apps where scaling is typically achieved by shared-nothing multi-threading making use of the receive-side-scaling feature of NICs.

Incoming packets are hashed by their 5-tuple and divided among CPUs and a thread is capturing traffic on each CPU and works independently of the others.

Edit: so the answer is that the question if thread safety isn't addressed, since it doesn't arise in the intended use-case. But I'm sure it could be added with per-bucket locking since it is based on cuckoo hash.