The chutney you have encountered is most likely one of the following
https://www.vegrecipesofindia.com/red-coconut-chutney-recipe...
https://cookpad.com/us/recipes/2615806-kerala-coconut-chutne...
A few minor points: the chutney is not a pickle in the sense of not being a fermented item, it's made and eaten fresh, just some ingredients ground up together, maybe fried lightly or not.
>mixing fermented rice and fermented dals
Close, but not quite. The rice and (urad/udid) dal (black gram - not black chickpea, a different species), are wet-ground together and then left to ferment overnight or so. Then the same flour/batter is used to make either idli or dosa. I don't have scientific evidence but idli is likely healthy, so is dosa, due to the fermentation, and idli is nice and light, as you noticed.
>I tried making it in my apartment but the fermentation failed a few times so I gave up.
Try asking an Indian or South Asian friend or acquaintance for advice, or ask on the IndianFood reddit.
Edit: Added Wikipedia links.
https://en.wikipedia.org/wiki/Idli
Tastes great with a coconut based chutney, or even a nice Spicey peanut sauce.