Besides the fact that the event text specifically mentions "slipping into the clouds", indicating the event is supposed to occur in a nebula, it wouldn't matter if it didn't: Nebulas have no bearing on quest beacons, or anything for that matter, unless you count exit beacons potential events being voided.
You neglect to mention the prerequisite of a slug crew member, which suggests that, either you weren't aware of that requirement, or you were, and that wasn't the issue. In the latter case, sensors level 2 is all you need; I can confirm that, since I never invest in level 3 sensors until the endgame, since they're more of a luxury than a necessity, especially on normal.