Cassiopeia Twin Fang and poison damage

Upon reading the patch notes of 4.21 it read that cassiopeia's twin fang amplified poison damage by 20% which stacks up to two times. The same reflected in the ingame tooltip. But as of 5.1 the tooltip got changed and now states cassiopeia's poison damage is only amplified. I might be blind or dumb, but I felt like it amplified poison damage for other sources too. Can you confirm if it never amplified poison damage from other sources such as teemo, singed and gift of the toadstool?

Here is the link to the patchnotes which states it amplifies "further POISON damage..." . And i've attached a screenshot of the in-game tooltip http://na.leagueoflegends.com/en/news/game-updates/patch/patch-421-notes#patch-cassiopeia