Hi, welcome to the forum, it can be restless leg syndrome or night starts (hypnic jerks). The causes of Restless leg syndrome are peripheral neuropathies, vitamin and minerals deficiencies, lumbosacral radiculopathy, spinal stenosis, excess caffeine intake, hypoglycemia, and hypothyroidism.
He needs to undergo spinal radio imaging, blood sugar and thyroid status to rule out the cause.
Pertaining to this I suggest him to consult a neurologist to rule out the cause and treatment accordingly. He may have to take vitamin B-complex supplementation. As such this would not be a matter of concern. Take care and regards.
If his leg movements look like the same movement repeated at regular intervals (like every 20 seconds, etc) then look up Periodic Limb Movement Disorder and see if this is something he needs to ask his doctor about.
Restless leg syndrome? A lot of people have it. Does he have a history of seizures? If not, I would look at the restless leg syndrome.
Brooke