I think the main point here needs to be that the entire notion of a canary only works if we can count on them being killed only for the purpose they were created. If it becomes acceptable to kill canaries because the signers are tired of signing them then we have a bit of a problem.
Now, for this specific case...
It sounds like you are arguing that a NSL has compelled them to make false statements. This seems fairly unlikely given what we know about the current legal situation. The idea that they may be lying for the sake of their business is more convincing.
However, if they are lying for whatever reason, why not just continue to sign the canary? The only plausible reason to do this is some sort of malicious compliance with a sloppily worded order compelling them to lie. It would make no sense for them to decide to lie for the sake of the business and then do all of this instead of just signing the canary.
If they have received a NSL this basically leaves two sequences of events, both of which contain some rather unlikely events. If I had to bet, I'd probably bet against them having received a NSL.
However, the canary should still be considered dead. They literally killed the canary. Their reasoning provided for it is really quite bad. Basically they ask users to trust their unsigned website because users already trust their (closed source) code. So they have either received a much more powerful NSL than thought legally possible, or are doing the worlds worst job of lying about not receiving a NSL, or they have not received a NSL and view a regular page on their website as a suitable alternative to their previous solution which involved three people in three different countries signing the canaries with keys stored on air-gapped computers. If you are counting on them for security, none of options are good.