Teemo poison stacks with Cass Passive?

Played a game of ARAm tonight and realized my stacks were getting kind of high.

Looked down and saw my stacks going up when I've literally done nothing. Then I looked and realized that every time a teemo shroom went off the Cass passive went up.

Is this intentional? This is not technically how its worded in the tooltip of her passive as it states "...targets she poisons...".