You have to remember only a couple sites are like Tapastic where you have "subs" and it's more of a recent thing--in the last couple of years. You can buy subs. Go to a place like Fiverr and you can get facebook, youtube, etc. It's not out of the realm of possibility that you can buy subs for any site.
I do think there is cheating going on with subs too. I haven't figured it out yet, but on Webtoons, when a see a comic with 1 update, and like 900 views but 600 subs, it's a bit questionable. Statistically, very unlikely. So yes, I do think there is cheating going on there too. I only recently took notice of this, so I haven't had the time to look into it more.
As far as cheating webcomics in general, it's been going on for years. You can buy pretty much anything...alexa, page views, upvotes, fb followers, tumblr followers, twitter followers, subscribers, etc.