Our world is three-dimensional, in the physical sense (length, width, depth). So what does the additional dimension (assuming that's what they mean) gain? Our visual system can't perceive any more than three, so what exactly are the folks behind this trying to express?
Perhaps they've found a way to have Bob travel in time? Many physicists believe that to be the fourth dimension.
Sounds more like a (very) silly marketing gimmick than anything else. Anyone who understands the most basic points of physics is going to be going "Huh?!" over this one, just as I did.
So Bob the Builder will be in 4D because it will use those sensory effects as well as a 3D film
However, just to be nit-picky, the 'D' implies another dimension. Smell is not a dimension; it's a sense. So yes, I still see "4D" as a marketing gimmick.
If the producers of such things wanted to be more accurate, they'd bill it as "full sensory" or something similar.
Keep the peace(es).