Tillie is absolutely right. At this point, further technical questions should go to your doctor for the specific answers that would satisfy you.
But Greg, I have good news. The neurologist examined you and decided there's nothing neurological going on that is worth worrying about.
Doctors are really smart. They're very good observers, too. (My wife was a doctor for twenty years.) They normally don't bother to explain their thought processes to patients because you couldn't possibly understand the underlying science without years of training.
All healthy people have benign phenomena from time to time (or permanently). I'm perfectly healthy, myself, but many parts of my body twitch every day. It's funny to look at. Your hyperreflexia didn't alarm your neuro. Some people just have hyper reflexes.
You asked about atrophy. It would help to understand the ALS process. Remember, in ALS, first the motor nerves in the brain and brain stem are destroyed, then the corresponding muscles no longer contract, and finally, the limp, unexercised muscles atrophy because they been totally unused, cut off from their nerve supply, for many weeks or months.
So first you would have a bad EMG, then later, obvious clinical weakness, and eventually you might see atrophy. Some ALS patients say they look like Holocaust survivors. My own wife's atrophy was hardly visible, because she was paralyzed for less than a year.
In your case, the EMG showed no problem with the motor nerves, the clinical exam showed no problem with clinical weakness to worry about, and the neurologist noticed no atrophy that concerned him. It doesn't get any better than that.
Trust me, a doctor is not going to put his license on the line if he suspects any possibility of a deadly disease.
If there is something wrong with you, you should return to your GP doctor and trust her to lead your health investigations, using whatever specialists she decides are needed.