Adding some context. Suni scored all of those points in the fall series with higher competition. Mäntykivi scored 5+2 in 5 games in the lower autumn series that Sato played in. Also noteworthy that Sato's teammates had better stats, though Sato missed some games to injury so it may not be a fair comparison. Karvinen (18 GP, 9+21, 1.67 P/G) and Latvala (17 GP, 10+17, 1.59 P/G).
Eliteprospects and other sites lump all of these separate stages together so it's hard to tell what kind of competition the players were playing against. You can check the separated stats
here. The website is in Finnish but it's mainly dropdowns.
Selecting the season and league (taso) should be easy enough. Nuorten SM-Liiga is Jr. A, and B-nuorten SM-sarja is Jr. B.
We can ignore the area (alue) dropdown since that's not used for the leagues we're interested in (Jr.A/B).
The important part is the series (sarja) dropdown where for Jr. B we have a couple of options: alkusarja, playoff, alempi jatkosarja, and confusingly just SM-sarja which is also the name of the whole league that encompasses all of these stages.
The season starts with the alkusarja with 16 teams, after playing everyone twice the bottom 6 drop down to alempi jatkosarja where they play with the four top Jr. B mestis teams (Sato's team KV was one of these). The top 10 teams of alkusarja make up SM-sarja. The playoff is just the playoffs of course, with one playoff spot up for grabs in the lower series for the top team. That's about it for Jr. B structure.