Firstly at that age they shouldn't really be aware they're being assessed-even for SATS in year 2 my dc were told they were playing at "Victorian Schools" and doing some work to show to the new junior school.
Secondly, I would expect their maths to be mostly if not all correct. They'll tailor what they give to the level, so it may be that your dc hasn't got the highest sheet.
I remember helping in year 1 and sometimes I would take different groups and you would have different levels of the same topic (so in time you might have one which is all o'clock, one which is o'clock or half past, and another sheet which is o'clock, quarter past, half past, quarter to etc). You didn't tell them they were doing different levels. I tended to treat it as part of the game. "Let's see, which sheet shall I choose... Oh! it's this one today!" The level you gave them, you would expect them to get pretty much all right. If they whizzed through them, then you might sometimes see what they thought of the next sheet. Sometimes they took one look and did it straight off, sometimes just the little step harder sent them into panic.
Thirdly. How do you know their assessment stuff was well above standard? I've had 3 dc, helped in class frequently, and I wouldn't be able to make such a judgement. I'm not a teacher.
Then we go onto the levels. Each level is very broad. It might be that they do meet exceeding in many ways, but not in one. It maybe that they're right at the top of the level but haven't quite gone that extra bit. It maybe that they can do more but the teacher hasn't got the evidence.
Next you have the support. Your child got that all correct. Great. But you don't know what support was needed. I've been with a group where one put their head down and did the whole lot straight off. Another would check with me first before writing the answer down ("is it nine?") which showed lack of confidence, and another needed taking through the steps and could do it broken down like that but didn't have the skills to go straight through. They all got all the questions correct, but their abilities were very different.
And lastly. Chill! What level his year 1 teacher assessed him as will never matter one iota. I can't even remember if we got a level in year 1. It should have no effect on their self esteem because what you tell them is you're really proud of them and their teacher thinks they're fantastic .