That to me suggests Napoleon did so against his first intention, therefore was reacting to Marmont's decision, therefore abdicated unconditionally because Marmont surrendered.
In honesty Alexander cannot be blamed for thinking the French army was losing faith in Napoleon, given the Marshal's initial ultimatum was to force an abdication and stop the war. True they hoped for better terms but they had seen the writing on the wall.
Marmont is almost as controversial as Bernadotte. He was isolated at the time, I recall, and could not have known the political situation unfolding at Fontainebleau. Yet having burned his bridges and incurred the suspicion of all and sundry, he shockingly voted for Ney's execution, which to me is the most foul deed.