It's a limitation in the way boards are indexed for searching.
For searches, non-word characters (e.g. slashes) are removed, so when you search for "/v/" you're really searching for any post where the letter "v" is surrounded by non-word characters.
This includes posts that contain "/v/", but would also include:>the "?v=" in "https://www.youtube.com/watch?v=">the "-V " in "Arc-V ">the " v." in "Marbury v. Madison">etc.
There's not an easy way to get around this other than subtracting any common false positives, e.g. by searching>"/v/" -youtube
so you don't see youtube links. But the issue there is that you'll miss posts that contain both a youtube link and "/v/". Another option is using Ctrl-F to search for "/v/" among the search results.