Not op but raita is just a thinned yogurt and cucumber. It’s one of those “made by feel” things so while there are online recipes with ratios it should be made to a texture you like. The cuke is usually shredded but can be minced or grated as well ( and combos exist as well). There’s a lot of variations which include other things like tomato, green chillies, or spices.
Op appears to have made a thicker version with some mint added.
The way it may have been written is not as upfront as scientific text is nowadays. Gelatin was used in ancient Egypt and agar (rather than agarose) was reportedly used as far back as the 1600s including for food.
https://en.m.wikipedia.org/wiki/Agar https://thecookingfacts.com/how-was-gelatin-invented/
I would also mention jams and jellies are in a similar fashion and the first known recipe for jam was written in the 4th century AD and it probably existed before then.