None of the words in the nonsense group actually means to talk nonsense as such. Babble means talking quickly, Jabber is similar but implies being difficult to understand - possibly by being foreign, ramble is to talk at length and largely without a point, and splutter means to attempt to talk but just making sounds instead. The nearest to "talking nonsense" is prattle, which is in the other group.
Speaking of which, it is my guess that at least a couple of words in the Twitter would not have made it on to Only Connect.

Good once the 'speech' lists were sorted.

The group about talking nonsense, in fact none of the words in that group mean that. Splutter isn't even about talking, if someone coughed after drinking they would splutter their tea for example.

In strict terms of the definition I'd agree, but I found the groups still get-able- so it affected the points more than the game play, I'd say. I liked how mixed up those particular groups were, it made the disentanglement all the more satisfying.

Apologies, the speech group should simply have been 'synonyms for talking' and not had the word nonsense in there, think I confused myself with the Lewis Carroll group. It's a shame you can't edit these after submission