There is a BIG difference between ACTIVATED abilities and TRIGGERED abilities. Only activated abilities can be activated, only triggered abilities can trigger. Activated abilities can never be triggered, and triggered abilities are never activated. Those terms are NOT synonymous. Meaning, Stuck in Summoner's Sanctum cannot stop triggered abilities.

Activated abilities ALWAYS use the template [cost]:[effect]. If an ability doesn't, it is not an activated ability, and thus unfazed by SiSS.

Triggered abilities ALWAYS use the words "when", "whenever", or "at" when describing their trigger conditions. An ability that doesn't use either of those words is not a triggered ability. Particularly the word "if" followed by a condition does NOT denote a triggered ability. Rather it is an indicator for a static ability that creates a replacement effect. Triggered abilities don't care about SiSS.