I'm confused...

You had a BP for 5C (aisle seat) and ended up in 5D (aisle seat, same row).

So what ?

EDIT: now I see, on "your" side of the aisle the middle seat was free but when you moved it was occupied. Welcome to my world where even as a GGL my elbows get cosy more often than not with a pax in B or E... And in any case you were only surfing on A's status so suck it up