Did you send him (or her) a private key or something?
Don't worry too much about it, he hasn't been active in 5 years and 6 days.
Nope,
just some random message, nothing really important.
But after I did - some thoughts came to my mind ;-)
Thoughts, that it should be a rule for all of the forums to not allow such usernames.
(for the security reasons.)
anyway,
It was locked due to inactivity. The original owner is obviously long gone.
So, it's good for the privacy of those mistakenly sent messages.
Best wishes.