Could someone have aspergers if they don't exhibit any traits but

I can't really say much about Asperger's as I am certainly not a professional, haven't ever met your friend, and it's particularly complicated for even professionals to diagnose Asperger's in adults. However, it sounds like your friend has been severely traumatized by the events of his childhood upbringing. I think also that it's possible that the professional that recommended your friend get screened for autistic spectrum disorder might have underestimated the extent of your friend's trauma. It's possible as well that the doctor may have recommended your friend get screened for autistic spectrum disorder in order to rule the condition out.

Regardless I think your friend needs to be seeing a mental health professional who has a level of expertise in treating Borderline personality disorder. There is somewhat of a genetic component to BPD as well as other personality disorders, mood disorders, and mental health disorders in general. Ideally your friend should go through a course of DPD which is Dialectical Behavioral therapy at least once, or even twice. There are also other types of specific therapies for BPD such as Schema-focused therapy, Mentalization-based therapy (MBT),
Systems training for emotional predictability and problem-solving (STEPPS), and Transference-focused psychotherapy (TFP). The only type of therapy with which I am familiar aside from DBP is STEPPS.

I hope it's alright if I ask you some questions. How old is your friend, is your friend currently living in a safe place away from his abusive father, and or other abusive family members? Was there any history of alcohol, or drug abuse in your friend's family of origin? Also you you feel comfortable sharing your friend's first name with me so I can pray for him?

Honestly? Coming from an aspie, it can hurt to find out that you're biologically disposed to be different to the point of a ton of things you actively worked on isn't normal. The grind to get there. It took me forever to get to the places where your buddy is, coming from a fellow person with PTSD. Eyecontact, understands sarcasm completely and easily, learned to keep talking about my special interests too much, etc. Still ramble too aha

Once someone's an adult, they've already grown and have figured out solutions to majority of their problems, or their aspergers would get diagnosed as something else. I was initially diagnosed at 4 years old, reconfirmed at 8, 12, 15, but at my pysche a few weeks before I hit 18, I got told that they wouldn't be able to rediagnose me 'cause I fixed majority of the criteria. Happens sometimes. Only my fellow aspies get the slightest suspicion I might be one, but anyone without gets really surprised when I tell.

Though what was it matter? Unless you also have it and want someone to confide to in it, there's no point in labeling your buddy with something or questioning a probable diagnosis. Just be happy for him going to therapy. I hope he gets better sometime.

EDIT: forgot to include that I have improper reactions to things still though, like smiling and laughing awkwardly in uncomfortable/bad situations, or generally acting inappropriate in terms of emotional response when I express myself, involuntarily.

Why don't you just let the doctors do the diagnosing rather than all this speculation about your friend and which label fits him? Sounds like a pointless exercise to me, can't you just be his friend?

Aspergers is hard to diagnose in an adult and can take a long time.
Taking into account Aspergers is hard to diagnose, even for a trained professional, do you think the average person would be able to notice the signs?

No.