The Walking Dead : I thought they needed all the explosives

What exactly happened at the end of the herd scene? I thought they were trying to steal all the explosives for the upcoming battle with the saviors, and they were going to leave the walkers on the highway to keep the saviors at bay. When the dynomite went off and Rosita said something about how that's not what she wanted to see, I thought Rick *beep* up and left a few sticks on the cable, and that the Saviors would be alerted and be on their tail.

But Michonne was like "we did it! I wuv you Rick!? I thought they were about to be in some deep *beep* Poking around where they shouldn't be.

The dynamites were old and probably sweating nitro.