It’s interesting that this random Lord makes a point of calling Osric “young.” Osric doesn’t seem young and maybe he isn’t. It’s possible that this lord is very old and everyone is young to him – though it doesn’t seem nice to send an old man to do your errands.
Why does the king send this guy instead?
It’s possible, of course, that Osric has been flustered by the exchange with Hamlet – but I doubt he’d have the authority to unselect himself for the message delivery job. It’s the king’s choice to send Osric and then not send him. It’s the king’s choice to send “lord” who describes Osric as “young.” Why?