Have you seen the template scheme?

Have you seen the save files? Kreg takes the Utopia on day 146. He can give away the army on the same day.
Regarding the rest. I already wrote how I reason. Nelka has a strong army and good stats. She clearly built them up in her territory. The question is, where is it more likely to find something valuable: in the treasures cleared by Nelka, or in the treasure and respawn point of the Pink player? I think the computers don't start taking Utopias before 3 months. Plus, there's an unexplored desert treasure.
Also, you can get seriously punished by Nelka. This is more likely than catching her while she's expanding. After all, she has one advantage: it's her territory, and she sees everything there. And we only see a small piece, we don't have any views, so we won't be able to track her.
There are suspicious moments in these actions, but judging by the save files, Britvotchka is not a very strong player, so there can't be any powerful intellectual logic in his actions. Most likely, after taking the Utopia in the swamp, he wasn't thinking about catching Nelka while she's expanding or something else. He just thought, "There's some darkness here, I'm nearby, let me jump in and see what I can find." Personally, I (and I seem to be so smart, like I know how to write a lot of text, but only on forums) would probably do the same in the game. Well, with a 50% probability, for sure.