Why does she always suspect something?

My wife is one of those who no matter what the situation is she's going to always suspect something else is going or may be going on.  I was at my daughter's apartment yesterday dropping off the gifts from her baby shower this past Sat.  She got so much stuff until it wouldn't fit in her car so I put it all in my SUV to drop off.  My daughter's roommate is a nice girl who has a 5 or 6 year old autistic son.  He's a very sweet little boy but he is completely non-verbal.  He only makes noises.  Well, I'vee been knowing this girl a little more than a year and when ever I see the little boy I'll wave at him or give him a little hug, something like that.  Autistic kids don't really warm up to people they don't know that well.  Anyway, while at my daughter's he walks out of the bedroom and stand next to me.  The next thing I know he reaches up and grabs my hand.  I go behind him and put my arms around him to give him a hug.  When I do he lifts his feet off the ground and I start playing with him.  I honestly thought it was the sweetest thing because he's never done that before.  When I got home and told my wife what happened she looked at me and basically said, "oh, is he thinking you're his daddy?"  She gave me the side eye like maybe I had gotten the girl pregnant and had secretly been hiding this kid from her.  She knows how to ruin a very sweet moment.