The ability he demonstrates in getting out of his manacles seem to point towards the Surges of Abrasion, Cohesion or Tension. The Surge of Progression could also fill that place (dislocating joints then using Regrowth to heal). But then again, simple Stormlight can also heal a lot as we see with Shallan repeatedly. If he is a Radiant and another Truthwatcher going by his eyes, Renarin might finally have a bigger role to play.
It is also possible that the General was already a lighteyes and just used the same eye drops that Tyn and Shallan did.
Or much more simply, he bonded a Shardblade.