Have you spoken to him and asked him?
I have 2 dc with ADHD and 2 with ADD, 2 of them especially can be really lazy. The other 2 are more likely to not complete the work due to concentration/muddled thoughts.
If my dc were on report, I would welcome any comments, especially the negative ones, as a way of gaining more insight and was of supporting dc AND teachers.
what has your ds said? Is he generally honest (with himself) about his performance and behaviour? Again, one of my dc ( a 'lazy' one!) would probably say the teacher was boring and they couldn't be bothered. Another (not lazy!) would say they were frustrated and couldn't concentrate etc.
Instead of being upset about emotive term, use the information.
btw, if on report, the teacher has probably got to scribble something in 2 seconds in the madness of lesson change-over, loads of kids rushing off, others trying to come in, check books are handed in etc. It was probably bedlam, and little time for fumbling round for the nicest wording. And if lazy is the 1st word, sounds like the teacher was frustrated.