This is sheer curiosity, not something that needs attention.
This
old thread shows two different members as 'thread starter.' Of course I thought perhaps two separate threads had been merged.
But look at its #1 and #2 posts. They're from the same date, though no time is shown, and from different members. They're the two posts marked 'thread starter.'
It's clear from reading #2 that it's a
reply to #1; it is
not the same issue posted as a question in a different thread, which then got merged.
So, how can two people be one thread's OP? If I had to bet, my money would go on it somehow having to do with both inactive members' label of 'guest.'