One definition of peaceful is synonymous, and one isn't. This is exactly why language has so many synonyms, each one is sliiiightly different. Choosing one intentionally instead of another is important.

In this instance, "peace" is being defined (not directly, but through context) as status quo, going about your day unhindered. "Violence" is being defined as causing direct physical harm to a person, and possibly property depending on who you ask.

With these definitions laid out, it's easy enough to see a situation that is not violent (no one got hurt at all) and also not peaceful (some people's days were interrupted) - one person mentioned blocking a road. This is a FANTASTIC example of non-peaceful non-violent protest. No one likes a pedant.