The short version, as I recall it, the motorcyclist had a helmet camera on and encountered what could have been interpreted as improper police actions against him. His camera was running. Later, after that incident, he posted the video.. complete with audio... on the internet. The LEOs saw it, and decided it was a wire-tap law violation ('felony') because the audio of the officer was recorded without his consent (illegal in MD). Had the motorcyclist not posted the video online, or not posted the audio portion of the video... he probably wouldn't have been charged (speculation).
At least thats my understanding, and recollection of that incident... it may have been slightly different then that.
Here is a good resource for recording laws by state:
Edit to add: Its important to note that audio reording laws vary by state. Some states are a 'one party' state.. you can record as long as you are a party to the conversation. Everyone in the conversation does not need to give consent. Other states, are 'all parties' must know/consent. Check the above listed website for details
Typical disclaimer.... not a lawyer, not legal advice, didn't sleep in a Holiday Inn last night.... lol