It means there are 25% more, but neurons aren’t the only thing the brain is made of. Idk how much of a size difference, if any, this makes. Considering how sensitive lips and fingers are compared to equal sized parts of your skin in other areas, there might be a similar situation of just having a lot of space in the total structure for extra neurons. It could be a small increase in size, it could have no impact on size, more studies required.