You are right!..Lots of agents can sound arrogant, Or be judged as such, but it's not really that. They are confident in what they like and often outspoken on blogs/twitter, but don't misread it as being rude.
I don't think its a horrible person, just beacause it's their view point!!
On the plus side...if they love your work, they will SHOUT about it in the same way!!!
Try following some more of them on twitter... even the excellent ones have tweets like.. " Slush pile is dire .. People, if you send to me, get it right..?! "
You'll soon learn that this is just "agent speak" and nothing more. No names are mentioned. It's just a call out to other agents who often tweet back similar responses!!..
Hope that helps.. 
I know quite a lot of publishing people - as I said, I know it doesn't represent all of them. This person really got my back up though!