Can spell effects NOT apply each other please?

So I just wrapped up a match and first of all, 3 different ap Champions with 3 completely different playstyles ( ) all built as either their first or second item and made the entire game hell so there's that. Anyway, at many, many points throughout the match Nidalee would whiff a spear and hit a minion, or someone would step on a trap and obviously it proc'd because that's how it works... and the echo proc applied Rylai's slow on someone she didn't even hit leading to them getting picked off when they rightfully shouldn't have even been in danger. Can this not happen please? Seriously?

P.s. auto applies slow too.