Hmm it's actually somewhere in between, it looks like about a quarter is sticker purchases, a quarter sponsored stickers, and a half in-app purchases. The above articles is off, if you read the link in the article it gives the breakdown above.
Maybe you should re-read the article.. it says 100m in revenue last quarter, of which 27m was from sticker sales (so 9m/month).
My mistake, shouldn't try to read articles pre-coffee.