RADIO:
If the FO keyed the mic, then the FO would be closer to that microphone, that was hot, and therefore louder. I can’t tell from the audio how close the speaker is to the microphone.
There are two hand mics, with a transmit switch on each. When pressed, that mic is the one connected to the radio panel, which then directs it to the radio.
There are also two boom mics, worn by the pilots, with a couple of transmit switches, which follow the same path to transmit.
So, four mics in the cockpit. My money is on the pedestal mic inadvertently being bumped by a knee, but other possibilities exist.
PROFESSIONAL STANDARDS:
If a pilot has an interpersonal issue with another pilot, there are company pathways to resolve that. There is an administrative oversight structure, usually with another pilot, known as a “Chief Pilot” at the head of that structure.
ALPA also has interpersonal conflict experts, a group of pilots trained in mediation and conflict resolution. ALPA would be my first call if I were to ever have a problem with another pilot.
In 23 years of airline flying, I haven’t needed to leverage those resources, but they’re well established and exist for just such a hypothetical conflict.
Companies have invested substantial resources in their flight crews. Far better to resolve conflict, or to rehabilitate a pilot with a problem, than to terminate. There are a lot of resources, in both the Union and company, that exist solely to enable pilots with a wide variety of personal issues to successfully resolve those issues and then return to the cockpit.