It's not always from how you talk, sometimes it's how your voice sound. It's rare you come across a white dude who sounds like Barry White. I can be on the phone with a client talking about fixing their computer. 7/10 times when I go and meet them for the 1st time I get "you sound black on the phone" and I have to imagine 1 or 2 of the remaining 3 were probably thinking it. I've literally gotten this a thousand times in my life if not more.
I like to ask why, and usually I get "your voice is too deep for a white guy"