That means these two particular broods haven't seen each other in that long. It doesn't mean no broods have coincided in the last two centuries, though that makes for punchier stories.

Based on the table linked in this thread, it's rare enough to be interesting on its own. Geographical overlap of broods emerging doesn't appear to have happened since 1998 and then only in Oklahoma.

But yeah, it's weather.com, they've been clickbait since not long after clickbait began.