The quest to liberate $300k of Bitcoin from an old zip file

Probably because it's trying to play a video ad.

Could it be accessing the microphone which causes a switch to the Bluetooth HSP profile?

Fingerprinting scripts often use the Web Audio API (see https://audiofingerprint.openwpm.com/). Sometimes, they use enough of the Web Audio API that the OS thinks they're trying to play audio, and it temporarily reduces the volume of other audio sources, sort of like when it makes your music quieter so you can hear GPS directions more clearly.

The line read something like 'he thought he'd have to charge 100k' so he made an estimation of the required costs of infrastructure and hours worked I think. He probably communicated the 100k more as a 'I cost this per hour and the machines would likely cost so-and-so would you agree to pay this or can we call it off?'.