I'll stick with Arbiters theory:
"The tl;dr to bot detection is that Jagex has developed (or can develop at any time) models for how humans behave (acceptable ranges for online time, algorithmic estimates for effects of tiredness, behavioral similarity to common botting practices, etc.) and have each of these models act as flags. Set off too many of these flags and you get the banhammer.
P.S. Oversimplification for verbosity's sake. Surely the flags are weighted, ranges statistically distributed, etc. As a disclaimer, these explanations are purely speculative, but if I know Jacmob half as well as I think I do and I am half as intelligent as he is, this is the way he would do it because it's the way I would do it.
P.S.S. All this being said, I would imagine most bot clients aren't even getting into the behavioral analysis portion. There is probably a tier one non-intensive analysis that is done to catch the clients that have fallen for Jagex's traps and/or utilize hacks/shortcuts that are easily detected. That would explain why certain bot clients are being called out by name by Jagex and accounts being banned simply for logging in through the client without even running a bot."