Russian mustard is usually made from the “white” mustard seed, which is more spicy. It is often made with vinegar, which preserves this spiciness. Vinegar is not typically used in other types of mustard; other types typically have additives that make the flavor of mustard seed proportionally less.
For example, dijon mustard uses wine or apple juice, and whole mustard seeds. When the seeds are not crushed, they do not release the inner spicy element. Russian mustard is made with pure mustard powder, a bit of sugar, water, salt, vegetable (usually sunflower seed) oil and vinegar. No preservatives are added.