I think Sakurai was just using that statement as a way of emphasing the distance that Rosalina can put between Luma and herself. Kind of like a remote controlled vehicle.
Rosalina's moveset has me really interested. Such a unique character.
When I first saw the trailer initially I thought that she had some moves that had "Super armor" properties e.g. take damage but zero knockback so the character remained stationary. However that wasn't the case when I watched again:
1:48 mark.
In fact Luma was taking the hit. Now here's a question, does that mean Rosalina & Luma share the same life gauge? Squirtle, Ivysaur & Charizard share the same life gauge but with Luma I'm not so sure.
In the trailer the Green Luma was hit by what seemed to be a fully charged smash attack from Mega Man and was KO'd, and the only way that a character can be knocked out of the stage like that is when they have already taken a lot of damage. However, just before that we saw the White Luma take a direct hit from Samus' charge shot (possibly fully charged) and yet was hardly knocked back at all.
So surely the Green Luma must have already had a higher damage % when compared to the White Luma.
Actually when you think about it they must share the same life gauge simply because you wouldn't get the varying knockback that we saw in the trailer.
We also know that Rosalina can "summon" different Luma types into battle as well. The trailer showcased five different coloured Lumas.
Yellow
Red
Green
White
Blue
Do the different coloured Lumas also share different properties? if one is KO'd does Rosalina have to wait some time before she can use it again?
She's a very interesting character.