It continues like this: "Use of the slash character to indicate hierarchy is only required when a URI will be used as the context for relative references [...]

It continues like this: "Use of the slash character to indicate hierarchy is only required when a URI will be used as the context for relative references [...] The path segments "." and ".." [...] are intended for use at the beginning of a relative-path reference (Section 4.2) to indicate relative position within the hierarchical tree of names. [...] Aside from dot-segments in hierarchical paths, a path segment is considered opaque by the generic syntax." As long as Wikipedia doesn't use relative paths it is not a problem to have slashes in the URL.