Also, perhaps you should understand their PoV, it is likely they have deeply thought something through and perhaps they find it best or understand that they simply do not need to communicate with you.
The difference between the population of those who have received a diagnosis and those who are on the spectrum is night and day, and it's often the line which separates whether you'll have any reasonable chance at life. The OP suspects his coworker has received such a diagnosis.
So when I hear OP say that his coworker may have a diagnosis, that absolutely changes the picture in my head. It's up to you to decide whether professional medical diagnosis is a signal to you.
Next time, please be more empathetic to the people who have not been diagnosed for whatever reason. "On the spectrum" means autistic. Whatever other interpretation you might want to give it is on yourself.