"On the spectrum" is both a soft term of art and very often a euphemism for either never seeking professional diagnosis or not being able to convince professionals that you warrant a diagnosis. It's also used to describe clusters of distressful symptoms which have not received a classification.

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.