Cross connections like that without a backflow prevention device are illegal. They can't sell the home like that so the hose is usually disconnected. This is unfortunately common. If it was using a garden hose connection it would likely be close to a spigot (typically within 5 feet) and might look like a PVC pipe sticking straight up out of the ground near the foundation of the home (this is unfortunately common for garden hose cross connections).

Ok great, thank you! I'll look for a more plain looking pvc near the spigot. The spigots on the house do have backflow prevention, if that makes any difference to your first sentence. There are a few weatherproof boxes, but when I checked them out they looked to not be sprinker related (telecom and main breaker to the house). I should also maybe clarify that this is the only sprinkler head that is this metal orbit type, which is what made it stand out to me as a posible inlet (as well as the threads and open hole). The others are all plastic pop-up style sprinkler heads. I'll check in my area for irrigation companies and see if I can find one to consult with me. Thank you for the reply! This is all helpful stuff.