Assessments- what's your experience?

My son had his NHS assessment at the beginning of the year and I'm wondering how it compares with other children's. 

He was 9 years old at the time and they did nothing with him except ask questions. He was with me and his father was taken to another room and interrogated, sorry, asked questions.  

That was it and took less than an hour including them discussing it after. They couldn't come to any decision on asd or adhd from that so eventually did a school observation ( not sure how long for, but NO longer than an hour) the day before school broke up for summer. 

They sent me a report saying he doesn't fit the criteria for either, but no actual explanation, despite lots of flags pointing at it in the report. 

I was expecting them to do some sort of activities with him and a physical, as well as a "profile" from everything I've read.