Given that there are many articles and lists of developmental milestones and  many lists of common characteristics for autism, and not all lists are consistent, some things which stood out in your post and would tend 
not to indicate autism include: 
1. pointing to the trees (non-verbal communication supportive of verbal communication) 
2. imaginative play
3. asking you to play with him (using intense interests as social currency)
Two links which may be of interest: 
postive traits of autism, 
recognizing ASD.  
Have you seen the SENG youtube  
video on The Misdiagnosis of Gifted Children?  There is also a related  
book which you may be familiar with, on Misdiagnosis and Dual Diagnoses.
You may wish to become familiar now with some of the support resources which may play a future role with advocacy for your child, such as the website  
wrightslaw, the  
book From Emotions to Advocacy, and National Center for Learning Disabilities (
NCLD). 
he is not speaking english yet, so they don know how he use of language
 What language(s) does he speak? Being an English language learner might partially explain his interest in learning reading at home but not at school. At three years old, what type of reading instruction is given at school?