Is Twitter use in freefall?

One developer has used the API to find Tweet volumes:

Tweets per day reached a peak in August 2014 of 661 million, our source says. That 30-day sampling period included the World Cup final. In January 2016, there were only 303 million tweets per day, on average, during the 30-day period.

Twitter (perhaps not surprisingly) says the figures aren’t accurate, but has not clarified any further.