Post lower blepharoplasty bag when I smile. Is this skin or muscle? (Photo)

There are a few issues here. At rest you don't appear to have redundant skin, so there is probably not much excess that could be removed or you might get an ectropion.  It looks like you had fat removed, so you are volume deficient.  This increases the amount of wrinkling when you smile.  Adding filler to the lower lid may help.  You could also do some laser resurfacing to try to improve the skin texture. Botox to the orbicularis will help soften the muscle roll you see under the lashes when  you smile. When people have a very large muscle here, a small amount of it can sometimes be removed.  If too much is taken it can affect your lid tone and blinking.    

You can tailor a muscle roll, reduce lower eyelid skin laxity and move up the we cheek junction with a superficial cheek lift.

It appears that you may be looking at your orbicularis oculi muscle, though pictures of you looking up would be helpful to see if it is fat, or bags.

Thank you for sharing your case and photos.  You have had the right amount of skin removed with surgery.  The bunching you see is from the underlying orbicularis oculi muscle. Some residual muscle is necessary to help you close your eyes and blink.  There are several options to treat this including surgery or Botox.  Consider a consultation with a board certified oculoplastic surgeon to discuss your options.  Good luck!

from your photo it appears you have had the maximum removal of skin as judge by your resting eyelid position.  There is always crinkling of the skin with smiling but you do appear to have more of a bag that is probably due to the muscle.  You could have your surgeon give you a trial of Botox injected into the muscle to see if you get improvement.  If you do then you could continue with botox if that is something you desire or have the muscle surgically debulked.  The surgery is relatively straight forward.  I hope this helps and best of luck.

It may be thickening of the orbicularis oculi muscle during contraction. It appears it may be more noticeable from a lack of smooth redistribution of the overlying skin during animation. This may be from the small amount of fibrosis/scarring that occurs after raising a skin-only flap to reduce lower eyelid skin wrinkles. This of course only if your surgeon used that technique. In either event, a carefully evaluated/planned/executed revision may well offer some improvement. If the question is primarily more informational then I would leave well enough alone.

The bag you see is most likely the Orbicularis muscle under the eye and trimming it may very well correct the problem and this can be performed very simply under local anesthesia.  Wrinkling of the lower eyelid skin is difficult to correct with a lower Blepharoplasty because the wrinkling is usually caused by sun damage, aging and excessive squinting.  One cannot remove enough skin or tighten the lid enough to correct the wrinkling.  It has to be treated with a chemical or laser peel to smooth that skin.