It's probably because people reported you. In almost every case i got my accounts banned, someone tried to talk to me just prior to see if I was playing. Also note they do delayed bans, so you may have already been caught at lvl 40 fishing for all you know. I have botted on my main before and never got a ban, but then i auto mine on my hardcore ironman once and catch a perm ban because some Rudolph wants to ask you why you're mining in Lumbridge swamp. I also caught a temp ban on mu UIM because i was using an auto mouse to drop all my fish, but i was still humanly here. Last thing before a 3 day ban was people talking about how i was always there and thinking i was a bot.
I would not run your software for long periods of time, especially if you dont have other skills nor quest points. This leads to more exposure. Bots must be reported by a player unless the team does some special sort of search - which is rare because innocents have been banned before. Using free scripts aside from combat will get you caught because anyone with half a brain will examine you and see you only have 1 skill. So, use those w temperance.
This is all advice based off my experience.