Teachers can be like that - cautious - i wouldnt worry the results to me show he is more than capable of the 11 plus - there are many dc's who leave primary and go off to grammar with similar results and your child has another year to go!
My dc is off to a medway grammar in sept. At the end of year 5 tests she was level 5 for english(writing and reading)- but only 4b at maths- wasnt told about science. Anyhow the teacher - who thought alot of my daughter- said virtually the same to me - she said they had lots of english of the right standard to put forward for an appeal if needed but not much maths at that point. She did say i should go ahead though - think she just wanted to put me in the picture.
When my dd went into year 6 dhe was working at level 5 in maths practically stright away - think they were tring to get some work of that level just incase it was needed - it wasnt as she passed and i expect you dc will too - stay positive - its the best way