He mentions in an earlier blog post [0] that the audio files are behind Cloudflare already so if Cloudflare did its job so I think the actual bandwidth impact on the origin server should have been pretty limited. Hopefully he'd turned on the option to ignore the query string to avoid the cache being bypassed.

I run a similar audio-heavy site [1] that's reached the front page of HN, also behind Cloudflare - the traffic spiking to terabytes a day is a bit of a shock at first but if everything's configured properly CF works well

[0] https://mynoise.net/blog.php#landed

[1] https://ambiph.one