Resignation when a draw is offered
In a recent online game, I offered a draw when the endgame is clearly drawing. To my surprise, instead of replying to my draw offer, my opponent resigned. I have no idea why they did so and my best guess is a misclick.
I am brainstorming and I guess there might be some possible scenarios that one may resign when a draw is offered:
In a tournament, if winning is the only meaningful result for a player while drawing and losing make virtually no difference to them. Seeing winning is hopeless, they may resign instead of accepting the draw offer.
A player is clearly losing while his opponent who does not need to win the game, or in a hurry to leave, offered a draw. Embarrassesd at this draw offer, the player chooses to resign instead.
A player chooses to lose a game on purpose, such as keeping their rating lower so that they can enter some tournament with a restriction on rating.
I have two questions related to this:
When a draw is offered, can a player resign as a reply? I think it should be technically legal for them to decline the draw offer first and resign on the next move, but is it legal to reply with resignation when a draw is offered?
Though extremely rare, is it considered unsporting (if legal at all) to resign at a draw offer?