Alemu is right. However, if your blocking reagent is milk and you want to reuse the primary antibody several times, I recommend using BSA instead of milk for diluting primary antibody.
Milk has casein and may not be suitable for phosphorilated proteins and it may de-phosphorilate them. If you are looking for phospho proteins, use BSA instead for blocking and for diluting the primary antibody. BSA is also better as it has a longer life-span so if you freeze your antibodies the chance of it being usable in the future is higher if you do this in BSA.
In answer to your question, I believe that Primary Antibody Dilution Buffer and Blocking Buffer in this case means the same.