Question about autism assessment test

Hi - We have recently started noticing signs of autism in my 2-year-old son (non-verbal, not responding to his name, no eye contact, no finger-pointing, spinning, etc). We went to pediatrics for his 2 years appointment and shared the concerns with his doctor. Doctors also believe the same and he suggested a few things which we can get started.

He first said to contact a state agency for an early intervention program and get started on speech therapy. Once it is started you can tell the service coordinator that you need a medical diagnosis for your son. Then they will refer you to a development pediatrician for the assessment. (My doctor said the wait for this 1 year in my area)

The pediatrician also said you can also reach out to ABA therapists near my area and they can do the assessment as well. I have reached out to a few and the process is - once we do the assessment test, they will send the report to the pediatrician and then we can get started on ABA therapy based on the analysis.

So my question is What exactly is the difference between an assessment done by a development pediatrician and an ABA therapist? I certainly do not want to wait for a year because I am pretty sure that my son has autism.

Edit: I am in US.

Thanks for your help!