Hmm, I don't know. I'm thinking he might just mean that the atmosphere of the overall sequel will be pretty consistent to how the first film feels.
He did talked about keeping the main characters designs intact going forward (hence the same characters part, even though he never did mentioned their designs when talking about them), and if it's going to have the same timeless feel as the original, it's a sign he's going to stick with the same designs and timeline for the 2nd film, I highly doubt he ages the family up at this point in time now that we have a definite plan in place (although if he does, it's probably going to be a 1 or 2 year gap, mostly to update Jack-Jack's role).
Plus Disney/Pixar rarely ever changes a character's overall design from their original film to sequel anyways (granted half of the sequels only had cars, toys, monsters and fish in them, this will be the 1st full sequel to have human leads).
Also the news articles are clearly positive that the family will likely stay in their current looks for now seeing as we just got the Superhero buzz as shown at the end of the 1st film, it'd feel very weird to start it off without explaining what happens after that.
EDIT: Talked to a guy on one of the articles (via Disqus) named Gerald Lopez who managed to talk to one of the Pixar animators regarding the Incredibles II about reusing the same character models from the original film to re-animate them for the 2nd film, and the animator replied back to him saying yes, they will.
Take it with a grain of salt for now, but it's something at least.