I really wish you didn't have that sentence in the article: "An individual who witnesses another person having a seizure should contact emergency medical services immediately."
For those of us who have regular seizures, the last thing we want to do is make a trip to the ER every time we have a seizure. Our son has one to three seizures each night (in spite of being on several medications and a special diet) -- believe me, we are not running down to the ER each night.
If you observe a seizure, the best thing to do is ease the person to their side, remove anything that could hurt the person if they bump into it, and try to get some sort of padding under the head. As long as the person comes out of the seizures within three minutes, and unless there is some sort of injury as a result of the seizure, it is NOT necessary to call 911. However, someone does need to stay with the person during the post-ictal stage, which may last 30 minutes or more, as they might be confused during this time.
A trip to the ER has actually been disastrous in the case of some with epilepsy. One person I know was rushed to the ER, and they were trying to hold him down (which is not what you do when someone is having a seizure), but in his confused state, he was fighting them off, and the ER staff ended up called the police who arrested him for assault. He ended up in a jail cell while he was still post-ictal, which could have been very dangerous.