Garbage advertised for some kind of profit, (views on youtube or likes or just attention in general) Not worth your attention in other words.
To elaborate, "Russian" mods are often poorly made meshslaps, which is exactly as it sounds, slapping a mesh and some textures onto an existing jbeam with poorly made or no edits at all. Private mods can be similar, but can also be decent. Private just means there wasn't a formal repo/forum release and was used by the original author or distributed by PM or something of the sort.
Russian mods are essentially low-quality mods you can get on third-party websites. They fit the definition of mesh-slaps, as they use outdated and unmodified JBeam structures; as a result, deformation is horrendous. Private mods are mods that are only used by a certain group of people, such as YouTubers. Quality varies from zero effort mesh-slaps to somewhat decent mods with edited/modified structures. As both Russian and private mods use models and textures from other games such as Forza, such mods aren't worth your time. Only download high-quality mods from the forums and the repository instead.
don't forget that private can also mean "too much of a giant baby to take any form of criticism" so they need to do all their work in an echo chamber or they just hate freedom