Referring to [0] where Asuras originally started out under the stewardship of Varuna but gradually the terminology changed to be synonymous with Rakshasa.
Do you have a reference to it being a mistaken translation? I'm a native Hindi speaker, and I would've told you asura and rakshasa are both demons. "Asura" == "not sura" == "not good" sounds generic, sure, but everyone grows up hearing that word only used for demons in mythological stories.
(This is far from the only case where a generic word ends up being used to refer to something specific that has that category. Everyone in Hindu mythological stories has a bajillion alternative names that are generic-sounding but only apply to them, based around some aspect of their personality or actions.)
Current Indian mythology has a lot of differences from ancient Indian mythology. The nature of asura is among them. Many of the then major gods were described in Rig Veda as asuras. Wikipedia gives a good overview: https://en.wikipedia.org/wiki/Asura
I used to think so as well till I read more about it. Asuras are equivalent to lords and divine beings equivalent to devas and not inherently evil. Even more interesting is how Asuras are treated in Budhism and in Hinduism-like religions that are prevelant in various parts of SE Asia.
0. https://en.wikipedia.org/wiki/Asura