I was just reading the errata on Unarmed attack and what's posted in the Roll20 Compendium is as follows...
"Instead of using a weapon to make a melee weapon Attack, you can use an Unarmed Strike: a punch, kick, head--butt, or similar forceful blow (none of which count as weapons). On a hit, an Unarmed Strike deals bludgeoning damage equal to 1 + your Strength modifier. You are proficient with your unarmed strikes."
I always assumed unarmed attacks did 1d3 damage not just 1 point. Melee attack also assumes Strength modifier unless otherwise noted BUT again I always assumed that you could use either. Learn something new every day... SOOOO for this games Houserules, Melee can use Strength or Dexterity and normal unarmed deals 1d2 plus the same modifier in bludgeoning damage. Martial Arts ups the damage and allows you to use a Bonus action to make another unarmed attack. Martial Arts Expert lets you make this extra unarmed attack as a free action. Re-reading my notes on Martial Art Expert that might not be clear which is why I think Davos made an extra melee attack... when it was suppose to be an extra unarmed melee attack roll... sorry I will edit.