Standing Leap is of questionable utility going by RAW. Pretty much everyone and their mother has Darkvision. Poison Resistance is a worse version of the similar Dwarf feature. Poison Skin is really the only standout feature here and it needs some mechanical reworking to make it less situational.

Is Grung an official race 5E?

The Grung are an official race, much like the Tortle and Locathah!

Are Grung a playable race?

It's a 4-page PDF devoted almost entirely to stat blocks for characters used in a streamed game session, and finishes with a half-page entry with traits for the Grung as a playable race. Thematically, grung are halfling-sized humanoid frog people with a rigid caste system based on the color of their skin.