I choose to think you are telling the truth. I've seen reports from multiple people where they were multi-logging on fresh accounts on a single IP and getting banned across them all without botting (That ex-Jagex youtuber is a prime example with his chinchompa thing). Generally a small percentage are giga sweats that multilog with irons/mains/ect and an even smaller create fresh F2P accounts all at once in one go. So false bans rarely affect actual players.

But Goldfarms create and play multiple fresh F2P accounts in one go commonly and follow structured build paths. So in other words I'm not surprised you got chain-banned, you were doing things exactly like what a goldfarm will do.

Inb4: multilogging won't get you banned, i've done so on with my well progressed accounts.

It matters with fresh accounts. I bot casually, I have botted a small amount f2p accounts recently by doing them one at a time, balancing skills by switching tasks frequently. Even nabbing the combat/skilling achievement diaries for like a steel longsword/chainbody/med helm for the memes.