Sivir's Shield does NOT block Gangplank's Parrley Ability

I just played a 60m team builder to learn Sivir and played against a Gangplank. Every google search I've seen has said that Sivir's shield does in fact block it but every time I use it right as he was coming at me it went straight thru my shield.

This GP was pretty strong and we won, but still it was very annoying. It is an ability he has and it should block that ability then. Their team tried to convince me that his pistol isn't an ability but I know it is. Even checked my GP in-game and it is his Q on the ability bar. Why can it not be blocked by Sivir's ability shield? It does not say spells specifically but "champion ability". It blocks everything else as far as I could tell. EVERYTHING else.

Other posts on the net have shown that shield blocks have changed every so often in patches so maybe it has changed for Sivir. If so it would be welcome to have them update Sivir's tooltip to say what it blocks since it is not any champion ability.