The wheel base is reduced by 5.5%, and the width is reduced by 5%. I couldn't find info on the actual maximum length changes, but according to these two sources:
Modern cars can be up to 5.6m length. Apparently this is not going to change much, so I wouldn't put weight into words "shorter" and "thinner". Yes, new cars are shorter and thinner. But is 5% enough?
Probably not enough, but a step in the right direction. I imagine this is the best they could do that also fit with all their plans for the new engines.