I'm going to answer this two different ways:
#1) It's not uncommon for Dragons to hold their feet up and flat while they are basking, it's a way for them to absorb more light and heat on their feet, and no, it's not a sign of MBD. It's just a normal basking behavior that they all do.
#2) If you have a young baby/juvenile Bearded Dragon that has been under a compact
UVB bulb his entire life, which is totally inadequate for a Bearded Dragon to begin with, as they need 13-14 hours of strong, intense, adequate wavelength
UVB light every single day, then he's gotten no adequate
UVB light at all his entire life up to this point. In addition, it looks like you have a glass tank, which probably has a mesh lid, and I'm sure that the compact
UVB light is on top of that mesh lid. All mesh screen tank lids block around 40% or more of the
UVb light, and since your compact
UVb light is already not emitting any adequate
UVb light to your Dragon, the mesh lid has ensured that he has gotten ZERO
UVB light his entire life.
So to answer your question as correctly and honestly as I can, no, the foot basking behavior is not a sign of MBD, but YES, your Dragon absolutely is suffering from a severe Calcium Deficiency, has weak bone density, and most likely has the start of MBD developing right now. This has to be true, as he needs 13-14 hours of adequate, strong
UVB light every single day of his life, and he's gotten absolutely none. (I don't know how old he is, but realize also that any and all compact and coil UVB lights, as well as the very weak T8 UVB tubes only emit
UVB light for at most 6 months, they all have a very fast UVB decay rate and as such all 3 of these
UVB light options must be replaced once every 6 months at the latest; I'm including the compact and coil UVB bulbs for the Tropical Reptile owners who can adequately use a compact or coil
UVB bulb, and for Beardie owners who use one of the many weak T8 UVB tubes that only last for 6 months, must be mounted underneath all mesh lids and totally unobstructed, and must be mounted within at least 6" of the Dragon's Basking Spot/Platform with a Metal Reflector inside the tube fixture in order for any adequate
UVB light to reach their Dragons from a T8 strength UVB tube)...
Your Dragon is not absorbing, processing, or using ANY of the Calcium, Vitamin D3, or any other nutrition that he's ingesting from his food or from any Calcium or Multivitamin powders. It doesn't matter how much Calcium or Multivitamin supplements you give him, without a proper UVB Tube (preferably a T5 strength UVB tube at this point, which will actually save you money as they only need replaced once every 12 months) over him for 13-14 hours every day, he's just excreting all of this nutrition out. You absolutely must get him a proper UVB Tube and matching tube fixture with a metal reflector inside it behind where the UVB tube sits immediately.
Bearded Dragons do 85-90% of their growing and developing during the first year of their lives, and then the rest during the second. I don't know how old your dragon is, he may be stunted in growth from the lack of
UVB light already, I don't know, but you need to be on the look out for tremors, shaking, any flipping over onto his back, unsteady gait while walking, etc. These are usually the first signs of severe and advanced MBD.
You can order a 22" Reptisun 10.0 T5HO UVB tube on Amazon.com for $24 (half the cost in any pet shop) and then add a 24" T5-rated (rated for at least 24 watts) tube fixture with a metal reflector inside it for around $28. So for around $50 shipped you can get him one of the best available UVB tubes and a proper fixture for it shipped. T5 UVB tubes only need replaced once every 12 months, only need to be mounted within at least 11" of his basking spot/platform, and can sit on top of the mesh lid, as they are strong enough to still emit adequate
UVB light to your dragon on the other side of the mesh lid (they are 24-26 watts versus the max of 13 watts that your current compact
UVB bulb is, so you see how bad this is)...I highly recommend that you order him a 10% or 10.0 T5 UVB tube that is at least 22" long along with a tube fixture for it immediately, while he's still young enough to reverse any damage that is already done....