My impression is that Google is not claiming a violation of terms, and certainly they have not stated an intention to take legal action. Google is claiming instead that any comparison of its own results with Bing's should be taken with the grain of salt that Bing (apparently) is not above "Googling" queries it doesn't have an answer to itself.
Hence why the last line of the official blog post on the matter is "we'd like for this practice to stop," and nothing stronger. This is PR, not litigation.