Indeed it's user input.
FWIW I set my own dates, even if I agree with the community... after all, later additions by others could significantly change the user average unbeknown to me.
I tend to find they lean on the cautious side overall, though it's worth bearing in mind that I do like maturity in wines. Although there are occasional instances of singleton windows that I'd very much disagree with, it is a useful community-led tool... for me more useful than the points, but each to their own.
One sanity check that can be useful, is to glance down the drinking windows for earlier vintages and indeed more usefully the recent tasting notes for your wine and earlier vintages. It helps give a good benchmark of ageing potential for a well-established wine.
Finally, although I do enter windows for all the vintage wines I have, the greatest use I have from them is for sorting the wines in order of relative maturity, so that when I'm looking to start drinking up some of the mature/over-mature wines, the more pressing candidates are grouped at the top. It's very rare that I pay close attention to the actual dates I entered, perhaps only when I have a few bottles and I re-adjust the window based on that experience.