I think it's human nature when in regular contact with someone you don't actually see, to build some sort of image in your mind as to what they might look like.
A job I was in years ago had me ringing customers and suppliers regularly. This was before the days of mobile phones so I could never ring who I wanted direct. My first contact was always lowly office staff, who would put me through to the person I wanted.
Over the years I would get to know the office staff quite well, usually women, and would always have a chat before they put me through to whoever I wanted to speak to.
On very rare occasions I would visit some of these companies and would finally get introduced to the person at the other end of the phone who I'd been chatting to for years.
And, as in your case with me, I was so way off the mark with my mental visualisation, I wasn't even remotely close, ever, lol.
On this forum I don't try and put an image to anyone really now, though I must admit back in the day when RD was active being bristly with everyone, for some reason I just expected him to look just like his avatar, Billy Jack, lol.