Yes, I once got out of jail similarly - booked a return trip but didn't notice that instead of coming back the next day, I was coming back a month later!

It was an easy-ish mistake to make since it spanned February month end, so I think selecting an outward of say 23rd Feb threw up the return portion already in the March calendar and I just clicked 24th (which was the right day of the week).

Didn't notice till I got to the airport and discovered all flights back on 24th were full and my ticket was non-changeable anyway. How I smiled when the outbound was cancelled.