Butter knife means a knife that is used to spread butter. They feature a dull edge and rounded point of some kind, as butter does not require a sharp edge to separate or spread. This particular kind of knife is not generally considered dangerous at all. So unless we're assuming that channel 4, which is well respected in the Bay Area, is fabricating facts about stories, it's not unreasonable to understand that they are in fact describing a dull, and generally safe knife.
Not only that, but this story has precedent. In 2005, in Omaha there was a fifth grader who brought a butter knife to school and was suspended due to the zero tolerance policy.
http://www.ketv.com/news/5027982/detail.html
This is an image of the knife in question for the second story. Notice the dull edge and rounded point, that are characteristics of a butter knife.