It's not a BIP39 seed, the number of words should be in multiples of three.
You can try importing priv_sipa as mentioned in that thread:
1. Install Electrum from
https://electrum.org/#download.
2. Install the wallet and initialize it.
3. Import Bitcoin Addresses or Private keys
4. Paste the priv_sipa in.
p2pkh:5...
p2pkh:L
p2pkh:K
I'm not sure whether they're using uncompressed or not but you can just substitute the characters after the semicolon with your private key.