This is an extremely late reply and you probably don't care or need this comment, but that's not actually what that means. It's true that this description isn't worded very well, but from what I understand, it's against the guidelines to create third party giveaways. What he is doing is creating giveaways on SG within a steam group and advertising his steam group in the desccription. Joining his group doesn't actually increase the chances of winning, at least not inherently and tbh I'm not sure why that's there, especially since it makes it sound like it increases your chance of winning THIS giveaway, which is flat out not true (maybe that's why he was suspended for a month? Or maybe something else) but it is true that you typically have a higher chance of winning a group giveaway compared to a regular one of an equal level.

I believe this rule is explicitly for stuff like Gleam or whatever, basically hiding the giveaway behind a service that would be profitable in some way outside of SG. That's why stuff like the jigidis/puzzles or quizzes are alright, since they don't give any advantage to the creator, just more effort for people who really want the games. Similarly, SGTools just narrows down the amount of people that can join, just like being in a whitelist, a higher level giveaway or a steam group.

Had these people made it so you'd have to follow their social media or steam group to get a LINK to the giveaway, that would be against the guidelines. But as far as I'm aware, you can advertise that you have a steam group and that there are giveaways being made for that steam group in SG. Granted, it's also possible this is more of a gray area and up to the moderator/admin if this is against the rules. I know at the very least, there are plenty of high profile threads advertising the existence of a steam group for SG giveaways and moderators don't seem to see those as an issue.

Here is the rule for descriptions for giveaways
"When creating a giveaway you are able to write a description. In this space you are welcome to advertise your products or services, including social media channels (e.g. Facebook, YouTube, Instagram, and Twitter), games, groups, curators, or other giveaways."
I could, of course, be completely wrong about everything, as someone who's not staff or heavily experienced in SG. However, this is how this all works as far as I understand it. If you can prove me wrong, I'll gladly accept a better understanding of the rules. Sorry for the wall of text.