I see a few other problems.
The first is wasting so much money on prosecuting someone who was walking on the street instead of sidewalk. Yes, they blocked the Brooklyn Bridge. But there is the Manhattan Bridge, Queensboro Bridge, Midtown Tunnel, and many other alternate routes from Manhattan to Long Island. The net impact was probably nothing. The sidewalk on the Brooklyn Bridge is woefully inadequate for everything anyway so I don't really blame them for using the road. Better to block cars that can divert at 60mph than bikes that have to divert at 3mph :)
The second issue I see is with the prosecution proving that a chain of custody was maintained for the messages that Twitter produced. If any Twitter employee has write access to the data store, the messages and timestamps could easily have been altered. How can the prosecution prove, beyond a reasonable doubt, that this did not happen?
Finally, how can one prove a tweet conveyed actual intent rather than mere interest? I often tweet about things like, "I should go get 5000 of my closest friends to block the Brooklyn Bridge." If I did that on the day of the protest, that would look bad for me. But I might have been posturing rather than organizing, which is my right to do without interference from the government.
Anyway, this is all a huge waste. It seems like New York City is being pressured to keep working on this bullshit case when they should have just cleared the bridge, issued fines, and moved on. Or maybe, you know, provide adequate pedestrian capacity so people can peaceably assemble without having to block traffic!
(Incidentally, the exact lane that the protesters blocked is closed every night for construction...)