It looks to me like your SMD pads are so close together that the space between the copper pads is too fine for the manufacturer to put a coating soldermask. It sounds like their proposed solution is to simply leave the areas around those fine pitch / small spaced pads exposed without soldermask (area in pink). I have had this type of change performed on past boards without issue.
While the soldermask does prevent solder from spreading, so also does a lack of copper. In this instance, as long as the space between your pads is void of copper on the same layer (which it looks like it is) then you should not be at great risk of shorting the pads due to this change, it just means that there will be a larger rectangle of exposed PCB around your pads which will not have the black soldermask - it should just be a visual drawback. UNLESS you have strict safety or military requirements which specify or require minimum soldermask for arcing or other reasons.
As long as this does not fall under one of those stricter requirements then I would first double check the library / package to ensure the pads are the correct size - make sure you didn't accidentally make them too wide, compare to the recommended layout in the datasheet - and if that double check works out, I would approve the proposed change.
