The tournament was a round robin tournament with 15 players and 15 rounds with each player get one bye. There are two sets of FIDE rating regulations, one for the period from July 2017 to December 2021 and one from January 2022. So, the first one is relevant here.
According to FIDE Rating Regulations effective from 1 July 2017 till 31 December 2021 (with amendments effective from 1 February 2021) the initial rating of an unrated player is calculated differently according to whether the tournament is round robin or Swiss. This is what it says for round robin:
8.2 Determining the Rating 'Ru' in a given event of a previously unrated player.
8.21 If an unrated player scores zero in his first event his score is disregarded.
First determine the average rating of his competition 'Rc'.
(a) In a Swiss or Team tournament: this is simply the average rating of his opponents.
(b) The results of both rated and unrated players in a round-robin tournament are taken into account. For unrated players, the average rating of the competition 'Rc' is also the tournament average 'Ra' determined as follows:
(i) Determine the average rating of the rated players 'Rar'.
(ii) Determine p for each of the rated players against all their opponents.
Then determine dp for each of these players.
Then determine the average of these dp = 'dpa'.
(iii) 'n' is the number of opponents.
Ra = Rar - dpa x n/(n+1)
What this complicated looking formula is trying to do is estimate how well the unrated players played against the rated players on average and adjust the average for the tournament taking this into account. The unrated player's performance is then calculated as if all the opponents had the same rating and that rating was the "adjusted" average rating taking into account the over all performance of the unrated players against the rated players.
The latest version of the rating document, FIDE Rating Regulations effective from 1 January 2022, makes no mention of any difference in calculation between round robin and Swiss. Here is what it says;
8.2 Determining the initial rating 'Ru' of a player.
8.2.1 If an unrated player scores zero in their first event this score is disregarded. Otherwise, their rating is calculated using all their results as in 7.1.4.
8.2.2 Ra is the average rating of the player's rated opponents.
8.2.3 If the player scores 50%, then Ru = Ra.
If they score more than 50%, then Ru = Ra + 20 for each half point scored over 50%.
If they score less than 50%, then Ru = Ra + dp
Ru is rounded to the nearest whole number.
So, it looks like the separate treatment of round robin and Swiss being scrapped.