I can guarantee you this is how most people manage to gain a huge following out of nowhere, at least on Webtoon.
Webtoon is home to a large audience of teenage and adult women, making any sort of anime-esque romance comic an instant hit. In my personal experience, I uploaded a 7-panel episode of my first ever romance comic with godawful art a couple years ago (imagine terrible anime proportions with scribbley line art and color), and I got 800 subs within the first week. No advertising, no mention of it anywhere; it was just a stupid little comic I made for my friends, which I hadn't even told them about yet. I got a bunch of comments along the lines of "omg the mc is soooo cute!!!11!!" and "i ship so hardddd!"
I ultimately dropped it because I hadn't expected such a huge response, and I didn't want the internet's first impression of me to be a poorly-drawn romance with little to no substance. I always figured that my popularity sprung from the decent anime thumbnail for my comic which caught the eye of people on fresh and drew them into the first episode. As far as I knew, no one shared it on social media.
But yeah, fun times. All you need to get a huge following is to cater to the largest demographic on the website you're posting on. I most likely wouldn't have gotten such a response on Tapas (I didn't know of the site at the time), because the main demographic is split between indie comics and BL. I've come to believe that subs and popularity shouldn't be a factor in deciding if you should continue your comic, though. Despite the influx of subscribers I got, I didn't enjoy making episodes for that comic at all, and I most likely would've burnt out sooner or later.
Make something you love, not something that's popular.