Although I am not certain beyond a reasonable doubt, I strongly believe that Gunthar is an alt of purchased (as of Feb 2015) account Hamuki, and was vouching for himself.

Archive of the bitcointalkaccountpricer.com page for Hamuki (selection is when I believe the account was most likely sold). Note the number of posts each activity period.

Gunthar's profile lists his BTC address as 1GuntharqyUPvE7NdXChiy8x6rFrH1woPe

Note that Hamuki's profile lists his BTC address as 1HamukiBbYq5Fe5mL2ZHCELemr4f7WHu6t and was last active on January 05, 2017, 11:46:12 PM

Both of these profile addresses are vanity addresses.

On Jan 6, 2017, Gunthar received a withdrawal from poloinex that was confirmed in block 446834. He later sent the entire amount of his BTC from his above withdrawal to an intermediary address, which transaction was confirmed in block 446879 (about 7 hours after the withdrawal). Roughly 7 hours later, Gunther sends the entire withdrawal amount to the address listed in Hamuki's profile. This transaction was sent on Jan 6, 2017 at 20:05, roughly 19 hours after Hamuki was last active, and ~3 days later has not logged back in to confirm payment (if you were going to argue this was a payment to him).

I can say on good authority that when Hamuki was sold that it's sale included the private key to one or more bitcoin addresses associated with it.