NTRU key size (confused)
I've thourgh that 439 would represent the key size in bits.


No, NTRU doesn't measure things like that.  Instead, it's the number of elements in a ring.  In addition, with the current parameter sets, each ring element is a value between 0 and 2047 (11 bits), and the public key consists of one ring, and so it takes up $11 \times 439 = 4829$ bits, which compresses to 604 bytes.