JW10 is the age group not the age grading. (It's set so that under 11s are identified - as mentioned above, under 11s have to be accompanied at parkrun (ie within sight of their adult). Minimum age you can register at is 4 or 5, can't remember which.)
The age grading changes for every year, whether you are 8 or 80 your age grade % (for the same time) changes every birthday - google for an age grade calculator and put some numbers in and you'll see.
Kids are welcome at parkruns and as long as they're enjoying it and the adult isn't pushing them to be fast. If they can't do the full distance (on a multi lap run) that's fine but they should not cross the finish line, it's a 5k event and if you don't do 5k you haven't finished.
The response does sound a bit snotty. My response would have been so say that we'd look at the results and if I agreed there was something wrong either change the results or say that we agree there's an issue but TBH don't know what to do to fix it and put a post out to explain. Results are fully editable at any time, so mistakes can be corrected afterwards.
If it was our results and it was obvious that something was wrong we would check the data and if necessary make an adjustment.
If there isn't an obvious error that can be corrected the solution would be to effectively annul them by adding, say, 30mins on to everyone so it's obvious that they aren't real, this would then set the PBs and course records to be the true ones.
We try hard to get the results right and if people mail to question a time it's usually helpful because it puts a piece of the jigsaw in place, rather than being seen as criticism.
Thanks Philomena, 10 mins before parkrun started Adam and I (parkrun event directors) looked at the vans on the course and general MiniMile set up chaos and wondered if we'd done the right thing! I then jogged down the hill so that I was ready to change the fences on the first corner and found someone had already changed them and our route was completely blocked - would have been parksteeplechase!
Luckily I had time to move them before the runners arrived.
Lots of good feedback on facebook so we were pleased to have done it.
Best complaint of the day - a runner came into the park and told a parkrun marshal (assuming she was BM) it was terrible that he couldn't do his normal route round the park because of all the runners/fences etc getting in his way. You can't please some people.