Why does the fact that he also used other names - which was often the case- makes you think that this alias was not inspired by the colonel who died at Austerlitz ?

I don't see your argument.

His other names may have been inspired by other people.

I even read that Mitterrand was inspired by reading the anecdote of Morland's post-mortem moustache in Marbot's memories - probably because Mitterrand had at that time a fake moustache.