They're not actually saying a warrant was served - that is an important detail that no one seems to be mentioning. All they're doing is not saying that a warrant wasn't served, and the two aren't the same thing.
There are a variety of circumstances under which the warrant canary would not be published. A warrant being served might be one (it might not), but there are certainly others: policy change being the most obvious.
I don't think there is a good legal precedent in general for maintaining that someone's failure to speak (under whatever circumstances) violates a provision for secrecy. I think that would be a hard argument to make, given that, at most, the failure to publish would lead some people to suspect that some kind of warrant had been served for something, somewhere, sometime in the past week or so, that rsync might have. Vague, at best.
There are a variety of circumstances under which the warrant canary would not be published. A warrant being served might be one (it might not), but there are certainly others: policy change being the most obvious.
I don't think there is a good legal precedent in general for maintaining that someone's failure to speak (under whatever circumstances) violates a provision for secrecy. I think that would be a hard argument to make, given that, at most, the failure to publish would lead some people to suspect that some kind of warrant had been served for something, somewhere, sometime in the past week or so, that rsync might have. Vague, at best.