Writeup ignores the nuances of mental health - there is a gradient between "I am definitely an imposter" and "I have imposter sydrome, these thoughts are not real". In between is a miasma of self-doubt and anxiety. And it can change depending on the time and the situation.
If a friend or colleague confided in me that they felt like an imposter (but weren't sure) I would treat that as a tremendous act of trust, not an attempt at 'humble bragging'.