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