What is special about an entropy count (RNDGETENTCNT) of 160 for libsodium initialization? (Moved from StackOverflow)

In the Usage documentation for libsodium, before calling the initialization function sodium_init, they suggest you check the entropy count of the system's CSPRNG (i.e. use ioctl to query RNDGETENTCNT). That makes sense. In the example code, they check that the entropy is at least 160. 

What's special about the 160 value?

The Linux CSPRNG now uses ChaCha20, right? But I would think that would require more than 160 bits of randomness to be initialized (e.g. it looks like the getrandom syscall in more-recent kernels blocks until it gets randomness of at least twice the ChaCha20 keylength, which would be 512 bits).
The internal RNG uses a 256 bit seed, and on Linux, a byte is read from /dev/random to check that the pool is seeded.

The reason for requiring 160 bits to be available without blocking is unrelated.

During initialisation, the library reads and discards 32 bits from the RNG to check that it is available and working.

Shortly after, it will need 128 extra bits for the canary protecting guarded memory allocations.

Hence, if 160 bits are not immediately available, sodium_init() will block. This will happen even if the application doesn't need to generate any keys.