Locking pawl broke allowing roller tube to rotate when wind got up under awning material.
An additional awning lock (be that a spring loaded pin, a wrap around type lock or just your awning rod stuck in grove on opposite end of roller and then lashed to arm) helps secure roller and takes some strain off OEM locking lever/pawl.
If you find yourself in that situation again (hopefully NOT) cut the awning material completely off with knife/razor blade...tear it off.
Awnings are cheap to repair/replace vs the danger on highway