As far as I know, if the seed is wrong the wallet will refuse to load the address. but why did he say the address seems empty?
before brute-forcing it, have you tried checking the wallet that contains the balance?
this is quite fishy, are you sure the seed is associated with an address that contains a balance inside of it? your friend might lie to you.
I don't know why he would lie to me, as far as I know he has no reason too.
The actual seed phrase he gave me checked out, but did not have any balance.
If the seed phrase that he gave to you is empty that means it has no balance or he has moved it out of the address. as I said before, did you know the address that contains the balance? if you know, check it first before doing brute-forcing because it is time-consuming (even I do not know it is going to work or not, I never used it to do this kind of thing. I used btcrecover to bruteforce the password).
I tried btcrecover, it could not recover the seed. And yes, the ETH is still in the original address.