But didn't the rule that that it must be at least 5 groups?
Yes, and this means
every possible solution to the level (excluding nuke glitches, so you don't have to worry about that) must create at least 5 groups. If any solution exists to your level where you end up with 4 or less groups yet still passes the level's % required, then the level does not satisfy the requirement of my challenge.
Another problem with your current level, although I'm sure you can fix it, is that the builder himself can be saved, and so if you have the first lemming as builder, he will not die with the next few lemmings as required by the rule.
But I saved the builder! I don't understand, sorry
Remember, we're counting consecutive lemmings in terms of when they
come out of the entrance trapdoor,
not when they reach the exit. So if you have the first lemming build and then he finishes and drops into the crowd, he is still the first lemming in my rules.
So right now in your level, if I make the first lemming out build at the right location, he will survive with the crowd, while the next few lemmings out will die while the bridge is not yet ready. As a result, you end up with the 1st lemming saved, while the 2nd, 3rd, etc. lemmings are killed. Whereas in my rules, the 1st 5 lemmings out must die in any solution to the level.