Comcast monitors Twitter
techcrunch.com
techcrunch.com
Someone at Comcast follows Arrington's tweets, or uses a service like Google Alerts. It might be for work, or it might just be for the same reasons any of us might do such things. Maybe that person emails the link to someone who is able to do something about it. The end.
(Running on a desktop machine right now, please be gentle)
Twitter is bigger than we imagine.
Yes, these are professional google searchers, looking for keywords and new hits on customers' brands.