It’s not designed to streak, but streaks aren’t that uncommon when looking at RNG as a whole.
Also, at lower player levels we actively STOP the RNG from streaking too much in the AIs favour when it comes to gem matches. (This pertains to waterfalls, and board control.)
I’ve asked the devs about percentage chances for spells, spawns, etc. EDIT TO ADD: The RNG is not DESIGNED to streak, but my guess is that there aren’t measures in place to completely stop streaking in these circumstances like there are for gem cascades at lower levels. In this case that would make it pure RNG. We haven’t purposefully made it streakier, as that wouldn’t benefit us or our players.