I think this theory goes a bit too far. I don't think there's been any direct deception on the part of the traveller, at least not yet. I do however think that there are only really two possible reasons for the other alien species to be chasing the traveller and combatting the humans. 1) the traveller is somehow offensive to them, so they want to destroy it and revert humanities advances. And this 'darkness' is just a term to refer to what reigns once the traveller is gone. 2) they want the traveller for themselves, to communicate and learn from it as the humans did. In this sense, these alien species might have followed the traveller through space and time (in the case of the vex) and want to kill the humans (and each other) and claim the traveller for themselves. Either because they learned about the traveller and searched it out. Or because the traveller already influenced them, and enabled their own Golden Ages, advancing them to be able to see it's powers and want more, however it left them, travelling as it does. And when it left, it altered them again, making them lose sense and lead to infighting and regression, or simply making them want to chase the traveller, to avoid the 'darkness' that's left in it's wake. I think either of these are possible. And that the traveller may well have left the humans too, but it never had the chance because the other species caught up and forced the collapse, maybe inadvertently. It's definitely interesting to think about and exciting to wait and find out in-game what the truth is. EDIT: As an after-thought, with the collapse, if the traveller didn't carry on travelling and stayed with the humans by intention, then there may be some overarching reason, other than that the traveller is racist or picky haha. But the traveller is definitely sentient in some way, whether it is a sentient being in itself, or if it's just a giant ship/space station, like a death-star except not a warship, and it's piloted by sentient beings.