Can head trauma (not severe) cause a stroke?

Yes, it is possible: Possibly a trauma caused a blood vessel in the head to tear. This can result in closing the vessel, causing a stroke. The process is called a dissection. Also, a bleed in the head (like a subdural hematoma) can cause symptoms that look like a stroke. These are all quite serious and need to be evaluated by a physician. You may need an mra to sort this out.

Occasionally yes.: If skull fracture might injure artery and either cause bleeding or thrombosis. Combination of head and associated neck injury could result in arterial dissection in neck and secondary brain infarction. Also, at least one report of internal brain vessel obstruction from a closed head injury.

No: Traumatic brain injury is defined as damage to the brain resulting from an external mechanical force, such as rapid acceleration or deceleration, impact, blast waves, or penetration by a projectile. Stroke would represent a non-traumatic brain injury which does not involve an external mechanical force.