The expression is maybe unfortunate because of the ambiguities in the word _rights_. However, the notion that non-human yet sentient beings deserve ethical and political consideration has become rather widespread and has developed a modest body of theory, whereas the position that they do not, wherever I have encountered it, has always appealed either to utility or convention -- in other words, it lacks philosophy. I'd be glad to speak as tediously as necessary for the former, if someone really wants me to -- I see animal rights or animal liberation as a natural extension of anarchism.
Gordon