I always tell parents whether their child is working 'at', 'below' or if they are 'exceeding' the expected level of attainment for that year group. If they are exceeding, parents will obviously know they're doing well and are achieving higher than the majority of the class (unless it's a particularly high attaining class). That's their own conclusion to draw though. I would never compare their achievements to that of the rest of the class by placing them 'top' or 'bottom', as it's none of their parent's business how the rest of the class are doing.
Personally, as a teacher, I have never stated 'top of the class' (even when it's clearly true). I just don't think the information is necessary for the parents to know, other than to use it to brag and boast. It also puts a lot of pressure on said child to stay there all year, if parents go around telling everyone their child is 'top of the class' (why would other people need to know that about someone else's child? I find it a bit cringe when people choose to share such information about their child with other people).
People do lie too, so I wouldn't always assume what someone says the teacher said to be 100% true. I've caught parents over the years telling people their child (currently in my class) is 'top of the class' after a parents evening or end of year report, when I absolutely never said that (and it's not even necessarily true!)
People often interpret 'top set' as 'top of the class', when it just means they're achieving broadly in line with 5 other kids who are all Greater Depth Standard in maths in that class.
I've had a parent in Reception interpret "they've settled in really well, have made lots of friends and they are enjoying their learning" as they are 'top of the class'. Someone else who knew them showed me how they'd put it all over Facebook that their 4 year old was 'top of the class' after the first parents evening in October. That child was quite average attaining within the class, but their parent chose to either interpret my encouragement the wrong way, or blatantly lie to their Facebook friends about how well their child was doing. Either way, it was quite strange and made me raise my eyebrows.
Basically, I would ignore any bragging from other parents and just focus on your own child. Working 'at' or 'exceeding' expectations is fantastic, depending on their future ambitions and goals. It doesn't matter where they compare to their peers, just keep encouraging them to do the best they can. Their best is absolutely good enough. It's not healthy to keep comparing their achievements to that of other children.