I've not watched any of them the times I've had Disney+ since I've got them all on Blu-ray so I can't personally say either way, but a quick Google search seems to indicate that it's probably down to some people mistaking the theatrical cut of Aliens with the Special Edition, and thinking stuff has been cut out as a result.
I'm not immediately seeing anything about the films actually being edited for Disney+ in the UK, but maybe someone who's actually watched them on there can say for certain.
Either way it kinda links up with another minor controversy recently about Disney+ editing, when people noticed that one or two episodes of Falcon and the Winter Soldier had seemingly had a couple of scenes edited for violence, despite having been available on Disney+ for about a year now. Disney said that it was a mistake and apparently changed them back, but it's yet another reason why it's going to suck if this doesn't get a physical release. I don't particularly like the idea of a company/studio etc. potentially changing their minds about something at some point in the future and then just immediately altering it because it only exists in the digital space.