No, it is not "common" on properly working bikes. It is safe to connect all green coded wires together. All these should connect to the battery Negative terminal (eventually), through the main harness.
The fact that you measure voltage on that open terminal means that something it is connected to, has a power connection on its other side. But, since it is disconnected, it won't operate because it has no "return" connection to form a complete current path.
Also, wires cannot be measured "Hot" with only one probe. You need two probes to take measurement. When state your probe point status also give the other probe connection, too.
Cheers,