2 1/2 year olds can be diagnosed with autism sometimes, but it is rare. I think they only diagnose that if the kid is having seizures and is totally living off in their own world. I have a 2 1/2 year old where the developmental pediatrician said "let's wait and see, and we probably won't know until age 5." It's better to wait and have an accurate diagnosis than to have them jump to an inaccurate conclusion. And in the early ages, it's more important that the children get help for their symptoms and what they are developmentally behind in than to have some sort of label. Screaming and pitching fits can be related to delayed language. Imagine yourself living in a foreign country, you don't know a word of the language, and you don't have any freedoms to do things like go drive a car or even go outside when you want to and the person who tells you you get to do something you still can't understand them, so it's like you don't know when you get to do things or what is expected of you. Man, I'd go nuts if I had to live like that. I'd be probably sitting in a corner crying my eyes out. Now, kids know that when they were babies and 1 year olds that crying and whining got them what they wanted. If they can't speak at 2, it's hard for them to learn that in order to get what they want they have to communicate in some other way. My daughter has learned sign language to communicate. It's bridging the gap right now, and I can tell you learning sign language is what has really made her tantrums less and less. I also have to tell her "use your words or use your hands to tell me" to remind her that she can communicate other than whining.
Really I don't know if my daughter has autism. She has a lot of autistic tendencies/traits and she still can't talk so much verbally. But, I really don't care to have a diagnosis, so long as she continues her therapy (she has speech, developmental, and occupational therapy one time a week each). At age 3, she will most likely go into a developmental preschool since she will still most likely be behind on speech at that point (it's 6 months away so who knows what might happen in 6 months, but we're figuring a complete miracle won't happen immediately). So, as long as they know, she's at such and such level with her speech and has certain OCD/sensory issues that also have to be worked on, then they are going to be doing what needs to be done, without a label slapped on her.
Anyways, be supportive of your friend, not criticizing her. If she is seeing a doctor to get her child looked at, she's ahead of a lot of other parents who don't even do that. Plus she's also getting a therapist to come. A lot of kids who are late with verbal skills are late to potty train. Cut her a break. I have been trying to potty train my daughter with absolutely no success at this point. How do you potty train someone who can't even understand you when you say "go get the ball"? She just understands one word commands at this point, not two or more words. So, we're slowly working on it, also doing things like reading potty books and watching a couple potty videos I got from the library. One of my nieces was a late talker. She wasn't potty trained until her 4th birthday. My sister learned to be patient. She dealt with a lot of friends and family criticizing her parenting skills and calling her a bad mother. Please don't do that to your friend. If her kid isn't potty trained until 4, that's her choice to let her kid go that long, no one elses. Sometimes having a little sanity to wait until the child is more verbal is more important than getting them to be potty trained by some text book defined time.
2 1/2 is too young to be that specific re: autism, much less the flavor of autism. Docs can't say much without more time to observe him. Granted, there is some developmental delay. The speech therepy is good. The speech therepist can refer him to connect him with services.
Screaming and throwing tantrums can be a trait, but more detail will help. Is your friend's 2 year old beginning to speak or use language?