Genie, my post might get a bit long, but stick with it 
Imagine you go to see a football game. You settle down to watch, and you expect to see a good game.
Suddenly you see a player picking up the ball - a definite foul. Yet, the referee says nothing.
Then, as the game continues, a player from the opposing team barges the one with the ball, again - a definite foul. Yet, the referee says nothing, and the crowd are cheering!
Once again, you are confused, and by now you are a little outraged.
The players are all over each other, barging, pushing, holding the ball and running. But the referee still doesn't intervene.
It isn't fair, it isn't right. They aren't following the rules. You just can't understand why they aren't doing anything about it, why they are letting it go on.
Suddenly, you realise that the game you are watching is Rugby, not Football. It all makes sense.
Probably a weird analogy, but you are watching a different 'game' than the teachers.
See your DS's actions from the teachers point of view:
She has a class of 30 children. She has a curriculum to get through, a class with wildly different abilities who all need to reach the same goal at the end of the year. Her target is 'end of year R' - they will all move on then.
So, lets see her day.
MasterGenie sits for snack time. He doesn't seem to like pear. He doesn't cause a fuss, but he makes it clear that pear is not his favourite thing. Fair enough, you can't like everything
He sees his Mum, and is unsettled, not surprising, he's young, just starting school it doesn't cause a problem for the class.
He leaves with Mum, doesn't really want to go not surprising, he was settled in the classroom.
He comes back settles quickly and quietly to the video he is not unduly disturbed by Mum leaving.
Now, you and I know that the reason he behaved in that way, was because he has ASD. But if he isn't causing a problem for the teacher, and he isn't disrupting the class, then disliking a pear or not waving good bye to Mum isn't a problem.
The real difficulty is that the social disengagement will hold him back from progress later, but right now, as long as he is 'passive' and grudgingly co-operative at school, it won't be seen as a problem for them.
You need to realise that this is Rugby, not Football. You can't walk into a Rugby game and say 'but their not following the football rules'.
You need to try and stop getting the teacher to see "ASD issues" - he has his dx. You know he has ASD. You know that the ASD causes him problems and difficulties. You have it in writing, and you don't need more proof than that.
What you need to be getting the teacher to see is "Educational Needs". So, you need to start getting evidence of how his ASD issues result in Educational Issues.
So why was it an educational issue that he didn't want his pear? You could say it was that he didn't make an appropriate choice in the first place; perhaps he doesn't like pear, so should never have been choosing pear, and needs help to make appropriate choices.
Why was it a problem that he put the pear in the fruit bowl, not the bin? Perhaps it was because he didn't understand the instruction, and that will cause him problems with whole class directed tasks. Perhaps he needs someone to personalise the instruction?
Why was it a problem that he sat in his usual corner? Perhaps it is because he is displaying rigidity, and that will cause him problems when another child chooses that corner? Perhaps he needs someone to spot rigid behaviours and encourage flexibility?
Why was it a problem that he didn't say goodbye to you or acknowledge you? Perhaps it was because he is passive and disengages from difficult social situations. Perhaps he needs support to encourage his engagement in social situations. Perhaps he needs someone to engineer small-scale social opportunities that he can then expand on?
Do you see what I am saying? It isn't enough to say 'did you see what he did then?' You have to be able to take it to the next level, which is what makes it a problem in educational terms.
Then, the school will have to act.
You must apply for a statutory assessment. You simply must. Nothing is going to change without it.