I think that most people don't understand the Glicko rating system. They are unfamiliar with terms like RD.
It doesn't surprise me at all that they can't explain it to you.
I think the reason that users show what you consider to be "unusual" starting ratings is that a rating is only shown after someone has played a game.
If they had described themselves as new to chess, their rating would combine the 400 starting level along with whatever points they had earned or lost from their first game. And since Chess.com ratings also include a change based on a statistical measure of their rating accuracy, the rating would have included that adjustment too.
Those adjustments are large when someone is new and they could easily result in a rating of 630 or 270 after one game.
A discussion about bots disguised at users was locked down. This is evidence that chess.com is trying to supress the fact that there are a large number of bots that are disguised as users.
I see new accounts that have peculiar ratings at the beginning, such as 630, 570, 230, and others that are not the standard starting levels. When I questioned one of these "users" about their starting rating it said it one rating is better than another rating. I pressed, it started talking about classes. I pressed more and it was giving odd responses, the way a bot does.
Chess.com is pumping up the user count with bots disguised as humans, thus defrauding advertisers.