My second follow-up article about prime numbers was published in Decoded Science as "Several Different Paths to Prime Numbers".
As always, I also publicize my articles in DeHaan Services. "Secrets of the Sieve of Eratosthenes" covers only the first of the articles. "Paths to Primes via Decoded Science" promotes the second.
First, accept your editor's advice unless she (or he) totally misses the point. In this case, I cheerfully accepted the advice to split the article.
Second, it's better to focus your article into one topic. Sometimes the topic needs an overview, and then a set of inter-related topics. Watch the overall word count: the article should be long enough that the readers are satisfied, but short enough that they get to the finish.