Why were you surprised? CR was and is an origin film. It would be madness to keep an aging Brosnan and have him make a movie that is supposed to predate all the movies that came before it. Brosnan's removal was and is logical.
There was a long period (well I can't recall how long it was) between the time Brosnan was confirmed to be out and EON announced the next film was to be Casino Royale. In between that time was when I was surprised.
I was surprised too when he was out because there was a time before they announced doing an adaptation of CR where Brosnan was going to make his 5th Bond film so I was very surprised when he was out since his Bond films did really well at the box office, sure they were not as successful as the Craig films but they still were pretty big hits, so when they got rid of him I was sort of surprised because I had thought a new Bond wouldn't happen until after Brosnan's 5th.
I don't believe a word of this for the reasons Zorin has mentioned and like mentioned before this is the same source that has said the Blofeld film is in production and a lot of this is based on a source with no official confirmation and some facts don't have an internet presence other than the Rotten Tomatoes source which makes the source very questionable. Like Zorin has said I am more worried about MGM's financial troubles than this excuse for a story.