In S1:E6 - Lethe Tilly has expressed an aspiration to be Captain one day.
In S1:E7 - Magic to Make the Sanest Man Go Mad - we see that Stamets is not affected by the time-loop because he has some ability to be outside the timeline.
Now there are a few possible explanations of what is going on in this situation:
(a) Stamets has overheard Tilly's ambitions that she talked about whilst jogging through the corridor, and it is at the front of his mind, and slipped out whilst he was speaking.
(b) Stamets has a visual impairment due the spore drive or his other work, and for a moment genuinely believed he perceived the Captain.
(c) Stamets was thinking "I have to tell the captain [something]" and that was at the front of his mind. When he saw Tilly there was a social trigger to speak, and the conversation with the Captain tumbled out.
(d) He actually is outside the timeline and was remembering something from another part of time/space.
My question is: Is Stamets calling Tilly 'Captain' an error due to the effects of the spore drive connection?