Brazilian butt lift. My surgeon told me my butt will continue to shrink, then the fat cells will stabilize and grow larger

Thank you for your question. With Brazilian butt lift we transfer fat from one area of the body to the other. These fat cells are transferred in microinjections throughout multiple planes in the buttock tissue so that they can gain new blood supply and live in their new home, providing increased volume and shape to the buttocks. After surgery there is a predictable swelling process that mostly resolves over two months, when the final result really settles in.  Around 70% of fat that is grafted is typically xpected to survive long term. 

Yes! Absolutely!   That is, if the procedure is done correctly!!!      I have been performing BBL surgeries for about 20 years now.      I have performed measurements on my patients of their waist and their Hips/Buttocks as well as their weight!     All my patients wake up with a buttocks that is significantly larger than it was before surgery.  If yours is not, then either you didn't have a BBL or your surgeon didn't put enough fat into it to be noticed!   This usually takes a large volume of fat!    What I have documented over and over, is that my patients buttocks will be significantly larger (usually several inches) when they wake up than before surgery.   Then as their swelling begins to subside, their buttocks will begin to shrink.   The waist and abdomen on the other hand, should be significantly smaller when you wake up.  Your abdomen, waist, flanks and your butt will all be swollen from surgery when you wake up.   All these areas will begin to shrink about a week or 2 after surgery.  The abdomen, waist and flanks will typically shrink and soften for up to 3 months as your swelling subsides.  The Buttocks area however, will typically only shrink for about the first 4-5 weeks.   Usually the hip/buttocks measurement at week 6 will show an increase over the prior couple weeks.  This is in spite of either maintaining or even losing weight!!!!!     This is what many people on Realself call "Fluffing".  I believe this is due to the volume of the new blood vessels that are forming, connecting to the new fat cells as well as the formation of new fat cells.  A large part of getting good results is thought to be the transfer of STEM CELLS!.  My technique includes transfer of stem cells to improve these results.   It has been shown that these stem cells will create more fat cells if this procedure is done correctly!   
So, Yes!   That statement is partially true.  6-8 months down the road, your buttocks may get larger, but this is probably only going to happen if you gain weight.  If the procedure is done correctly, your buttocks should be significantly larger and your waistline should be significantly smaller than it was before surgery.  To do this procedure correctly, My Techniques takes about 6 hours on average!   It takes longer than many surgeons, but, I have seen many of my patients back 10 years or longer after surgery and their hip/butt measurements still remain about the same as their measurement at 3 months as long as their weight remains about the same as well!   My technique works!   Permanently!