PTSD is triggered by a traumatic event or series of traumatic events, and it seems like if that happened to a person with chronic adjustment disorder, he or she could get PTSD, just the same way a person without chronic adjustment disorder could.
When the military assessed those who got PTSD it turned out most of them had some mental issues before joining the military, which would accord with what we see in life. Everybody in life goes through some really rough stuff at some point, but most don't get chronic issues like PTSD because of that. If they did, humans probably wouldn't still be around. So it would stand to reason that having any preexisting mental issue would make one more likely to get PTSD. That being said, this is a highly misdiagnosed disorder. Some use the term colloquially, even mental health professionals. Not every emotional reaction to something that happens is PTSD. Most isn't. You don't mention what it is you have PTSD about, so we can't say much about what's going on with you, but the fact a psychiatrist said that doesn't mean you have it. But you might. It would depend on your symptoms and the circumstances leading to those symptoms. A lot of psychiatrists are pretty conservative about labeling things and are good at what they do. But like anyone else, a lot of them are quite lazy and uneducated about psychology and are more drug purveyors than anything else, so again, the mere fact someone labeled you as having that disorder doesn't make it so and doesn't make it not so. There are psychologists who specialize in diagnosing and treating PTSD, as the treatment has some modalities that differ from the treatment of other disorders that might have similar symptoms. As the above states, PTSD is triggered by events but not necessarily caused by them. So yeah, you could have it, and yeah, you might not. It depends on what has gone on in your life and how you reacted to it. Peace.
New diagnoses can be helpful for figuring out the right direction. I'm glad you are seeing a psychiatrist to help you and would imagine a psychologist as well? If not, that would be best. https://www.webmd.com/mental-health/what-are-treatments-for-posttraumatic-stress-disorder They do a pretty good job of treating ptsd these days. My son has symptoms of ptsd but is not treated for it. He was bullied in school and had such a bad experience overall, that his high school is triggering to him. To the point of full on panic attack. We're working on this and our options for what to do next year. He didn't really have a single trauma or even trauma a lot of people would consider trauma. But he is none the less, traumatized. He's lived with anxiety and other things for many years now and it's been hard on him. The link that you can copy into your browser has some different forms of psychotherapy that they use including cognitive processing therapy which is interesting and involves going over events and then writing about them to process it. There is also exposure therapy. I find those most interesting.
Anyway, in answer to your question, a long time situation of adjustment disorder can lead to symptoms of ptsd as life in itself probably feels fragile and traumatic to you.