You're getting 9*240= 2160W (more or less depending on your actual voltage), which seems low, but could be okay depending on the actual element used. It's not 18A. All of the current that goes in one side, goes out the other, so they don't add as was said. Essentially, you're measuring along the same wire. It gets a bit more complicated if it's a 3-phase circuit, but essentially, it's a one-phase. 120vac is sort of a fake result of the way the power is supplied. You're actually being supplied with 240vac with a middle tap (neutral) from the transformer.
Using and understanding test equipment is critical to getting good indications. Heating elements tend to short or open when they're not working right. Their actual cold resistance will change a bit as they heat up, but will give you a good rough idea you can test. Just make sure the power is off and you've removed the incoming wires.