There's no reason to mention the summer of '78 because it wasn't relevant to this story. You don't need to watch the other three to watch this one. While the Fear Street books take place in the same location, they're not published in a chronological timeline. There is zero reason to bog down every installment with rehashes and flashbacks of the first trilogy. So, no. There is no "confusing plot hole." More like a confused watcher desperate for content for their website.