Playing through this mod I just reached the point of launching my first Excavation Drone and completing the technology "Checkpoint: Excavation drone demonstration". The first time I launched a drone I did not pay attention to how large the area would be, and destroyed part of my base (my bad), but also got the multi-paragraph text beginning "You've completed the first phase of your mission by establishing a large and..."

I loaded an auto-save and fired the excavation drone at a safe area. It still said I completed the technology, but did not display the paragraphs.

I have preserved that save and loaded it a number of times, and I can consistently reproduce the issue. Based on where on the map I fire the drone it does or doesn't display the paragraphs. Each location is repeatable on whether it does or doesn't, but I cannot find any rhyme or reason to which spots on the map will trigger the paragraphs.

I believe that it comes down to whether you're excavating a region that gives you terraforming points. You make progress toward one of your end game objectives when you replace exotic terrain as explained in the terraforming drone tooltip. Once you launch a rocket or start achieving end game victory conditions it unlocks the mission panel and gives that introduction. You get an excavation drone pretty close to the same point you can launch a rocket, so usually it's not a major distinction which one triggers it. The excavation drone objective is not a prerequisite for launching a rocket, and not every place you can launch it will score terraforming points, so not everyone unlocks the end game with that.