You meant 763 right? 762 is either domestic J or 2-2-1 config (so "A" is not a single seat).

If the agent told you 5A was a single seat, looks like you got the best seat on the whole plane! [I would say it's even better than 8K if you don't care about PTV] It's an ex-CP plane. That seat reclines almost into a flat bed because it's used for relief pilot on long flights. The only thing is there's no window next to that seat.