If someone used the same name that I am using for an internet nickname for myself (a person) for their company, I would essentially not care. At worst I'd be annoyed at an increased number of "@" mentions that comes from there being namespace collision.
And, frankly, this happens all the time. There is a ton of name collision out there happening as names which are sufficiently unique for a local context get moved online, which is a global context. Generally, when people find out there's been some name confusion, they are mildly annoyed by the inconvenience of people "@" messaging the wrong account, but not indignant that someone dared use the same name as them. Mostly when I see this happen I see people getting upset about the people "@" messaging them not checking the name more carefully, not at the company for picking the name. That is a pretty strong indicator, to me, that most people wouldn't consider this a "dick move".
Would you be annoyed/angry if someone took your twitter handle and primary domain name and started using it as their own? If though you are very active and controlled that name for a number of years?
Almost everyone would be angry (or very annoyed). There are a limitless number of names out there.
Here is why it is a dick move.
1) They almost for sure knew about him and his name.
2) They didn't contact him or offer to buy out his domain/handle.
3) They went ahead with it anyways probably because he hadn't trademarked it.
Look it's not the end of the world, it's just a pretty shitty thing to do to a person.