I don't know what you mean when you say 'was I diagnosable' nor what your therapist meant. In the end, an autistic spectrum diagnosis is an opinion, a professional opinion.

An online test is just something someone puts online. The questions can be wrong, the threshold for how many questions need to have the 'autistic answer' for a certain test result can be wrong. And in the end since you yourself put in the answers, it will only tell you how autistic, or not, you yourself perceive yourself. If the test is actually reliable, you need people that know as much as possible about you to answer the questions for you.

Don't let online tests, or things people online say, make you feel like you have a certain diagnosis. In the same way, also don't let them think the issues you are facing are not real problems that need real solutions.