I don’t think that Callum here has been around since 1969. Or 2069! Time traveller!
To extend this, if a forum account hasn’t been logged into since the migration, it is assigned an Epoch time of -1 which is a placeholder value for if no valid date can be assigned to the account. This -1 translates to standard calendar time as December 31st, 1969 which is what is shown on the account’s profile.
I guess the Discourse people decided to let the -1 go through instead of catching it and displaying some sort of error message like “Unknown” or “Long Ago” or something along those lines.
Somebody should tell them that.