Osmocote, Osmocote Plus, Dynamite, and others are controlled release fertilizers that rely on temperature rather than water to release nutrients. So, the label is correct in the sense that it won't be positively or negatively affected by water. It will release nutrients regardless.
On a related note, if you ever dig around in your gravel and find little Osmocote pellets, it's not because the fertilizer isn't dissolving. It's because the boding agents that hold the pellets together aren't dissolving. The nutrients are long gone.
For what it's worth, my dad, a certified crop adviser specializing in ornamentals with over thirty years of growing and fertilizer experience, likes Dynamite products over Osmocote because of the bonding and releasing agents that Dynamite employs. According to him, Dynamite has a much more steady and stable releasing timeline than Osmocote.