The strange behaviour sometimes encountered on the school run can take some getting used.
Ds is now in Y5 and I've perfected my technique to mirror the behaviour of others. For instance, there is one parent who never EVER acknowledges me, I've tried to make eye contact with her, tried to say a friendly 'morning' but nope, I have to imagine she has 10,000 things running through her mind on the school run, so now I just breeze past her. Added to the fact that she never responded to a party invite, with a yes or a no, when I know she had the invite in her hand, so know she received it, I'm really not losing out on the friendship of the century here.
There are other school Mums who smile and say 'morning'or 'hello' as I do, others who I chat to on and off, others who sometimes walk right past me with no acknowledgment but then other days do. Again, I can imagine there's lots going on in their heads, as I've also rushed by thoughts elsewhere, never meaning to be rude, there's just been moments of complete head in the shed. Doesn't happen often though.
OP, it's hard navigating through primary school life. It's not just about your dc, it's also about surviving the playground politics. You will learn to grow thicker skin and shrug your shoulders to the weird and wonderful behaviour of some parents.