Dont waste your time explaining or justifying yourself to someone who is clearly ignorant. Part of going natural is that you have to develop thick skin and decide you dont give a $:@/ what people think because It is your God given hair and you love it. We call transition more of a mental than physical process because you have to develop a new sense of what is beautiful. Your manager is still in the old mentality.
You are probably going to hear a lot more negative comments from people maybe even family members so you have to decide how you will handle it. My aunt told me yesterday I need to comb my hair. Whatevs especially since She was wearing a tacky wig.

If you need to vent come on here and rant. stay employed.