Parenting assumptions

I love Kat. I may be overwhelmed by her at times. OK, most of the time. It is still sinking in that I am responsible for growing a person. ME. I cannot even organize my desk at work. And I am supposed to grow a responsible adult? This should be interesting. Anyway.
I love spending time with Kat. Last night she fell asleep curled up in my arms on my lap. She looked so peaceful. I held her til Wife came and got her and put her to bed.
On Tuesdays Wife has class in the evening. So I take Kat to daycare and get to pick her up after work on Tuesdays. I get to be primary caregiver for an evening. It is fun. I feed her and play with her, change her and put her to bed. (although tonight she did NOT want to take a nap. she fought her nap til she was really hungry, then after she ate she STILL did not want to go to sleep. her eyes are all red rimmed and she looks so tired)
During the day today a work acquaintance asked if I had plans this evening. So I told him about how I get to pick up Kat and spend the evening with her. Feed her, play with her, spend the evening with her. I kind of talked about it a bit, how much I enjoy it and how I was looking forward to my evening with her.
The co-worker looked at me and said, "Oh, I didn't even know you were divorced."

I thought this was pretty strange. Then I thought about what it means that people think this way. Is it that unusual that a dad looks forward to spending his evening with his daughter? Does an evening described taking care of Kat need to imply that there is no Wife/mother in the picture? That I am a single dad or that I have joint custody of my Kat?
I went on to explain that Wife has class on Tuesdays and that this is one way I support her schooling.
But I still think it was a strange reaction.