Hello & thanks for your Q on HCM
It seem that your student is having purpura
( disorder of platelets in blood causing easy bleeding through blood vessles )
In children of his age it may be related to preceeding viral infection Or may even be due to autoimmune condition affecting platelets.
I suggest he must have a blood test
(blood count, liver
function, clotting screen) done along with urine test ( to make sure there is no blood in urine)
I hope him a speedy recovery