Oh no! That's very concerning and I hope you can find some good input!
Basenjis are notoriously "one person" dogs. Is he usually with someone else in the family (you?) - meaning, who do you believe he thinks is "his person"? I ask because while my basenji otherwise adored my husband, when I was distraught or unwell she would become defensive if he did anything she perceived as him trying to separate her from me.
Another thing to consider, if your daughter is old enough, was she menstruating? I know, it's an odd question. I don't have any experience with male basenjis but my parents had a male Boston Terrier that would get weirdly defensive when it was my "time". It looked like aggression though I thought perhaps it was more his screwy way of trying to herd/control my movements. It's a weird possibility but maybe something to consider if other things don't make sense.
I've found with mixed breed Basenjis often the real "tells" are...the very distinctive goofy behaviors. For some reason the silly way of sitting, that particular basenji head-tilt, and habits like wanting to sit/lay practically on top of their chosen person/people seem to carry over more than vocalizations or lack thereof, curly tail, or even eyebrow wrinkles.
So if she's elegant one second and then the most elegant goofball you've ever seen the next maybe she's got some basenji in her!
My name is Merry and I live in the Seattle area. Currently I do not have a basenji but I had a girl named Tano for 16 years. She was my best friend ever and I will never forget her - the good and the bad.
It's great to see everyone sharing stories and photos of their dogs!