a seed which is a bunch of human-readable words.
There is a difference between a "seed phrase" and a "seed number". The latter is generated from the former (or generated randomly if no seed phrase is used).
Electrum doeesn't always follow the usual BIPs but we can look at BIP-39 to see how a seed can be generated from a seed-phrase
To create a binary seed from the mnemonic, we use the PBKDF2 function with a mnemonic sentence (in UTF-8 NFKD) used as the password and the string "mnemonic" + passphrase (again in UTF-8 NFKD) used as the salt. The iteration count is set to 2048 and HMAC-SHA512 is used as the pseudo-random function. The length of the derived key is 512 bits (= 64 bytes).
Note that 64 bytes can be written as 128 hexadecimal characters.
Note also the distinction between seed-phrase and passphrase. These are two different things that are both used (though the passphrase may be empty).
the seed is like a 129-length string, it looks like a hash. Is that a hash?
According to Wikipedia
PBKDF2 applies a pseudorandom function, such as hash-based message authentication code (HMAC), to the input password or passphrase along with a salt value and repeats the process many times to produce a derived key,
So yes, hashing operations are involved. The seed isn't a simple hash of the seed-phase though.
Can [the seed number] be used to restore an Electrum wallet?
So far as I can tell, Electrum provides a way to restore from a seed-phrase but not from a seed number.