The rating document is for regular ratings. Maybe they use slightly different rules for rapid and blitz?
FIDE Rating Question

I suppose that's an option. I've emailed them (yesterday, thus far no reply), and I'll post any answer I get here as the guidelines on this seem less than clear.

I know the rating itself will be different, but I thought that the method of its calculation would be the same as for Standard.

Found the answer. K factor for Rapid and Blitz is always 20:
https://www.fide.com/component/content/article/1-fide-news/5721-rapid-and-blitz-rating-lists.html
I am a little confused about the calculation of my rapid rating. Before this month I did not have a rapid rating, but since I played in one tournament this month, I have one now based on my performance in that.
1. My standard rating appears to have been used as if it were my rapid rating from the previous month, with this month's rating being based off an adjustment of that rating in the normal fashion. Is this normal?
2. More confusingly, my K value (development coefficient) appears to have been set at 20. From what I understand in the FIDE rating adjustment guidelines, Article 8.56, it should be 40, as:
(i) I am under 18 years of age with a rating of less than 2300.
(ii) I have not yet played 30 games of FIDE rated chess, even if my rapid games from this month are taken into account.
Both of these would result in a K value of 40. So why has mine been given as 20?