Let's look at the overall chronology of how this exclusivity story came about :
1. Multiple indie games were announced at Gamescom as "First on Xbox." There was very clear implication that the exclusivity of said games were timed.
2. ROTR was announced as "Exclusive on Xbox, launching Holiday 2015." There was massive confusion from the get-go, because Point (1)'s language was used to announced timed-exclusives, but ROTR had a different language that implied bonafide exclusivity.
3. Games media didn't immediately buy into the announcement. When MS PR was pressed for a statement on the matter, folks like Geoff, etc clarify that MS refused to budge from the very "fixed statement" of "Exclusive on Xbox, launching holiday 2015."
4. Crystal Dynamics posted an article explaining the exclusivity, except they called it an exclusive, ( without the holiday 2015 line and no PR-safe terminology), which immediately prompted fans to suddenly get confused over the state of the game's exclusivity.
5. At the same time, CD effectively drew anger from Playstation/PC fans by saying "Don't worry, Temple of Osiris for y'all to play!" in that same post.
6. Aaron Greenberg also referred to the post by CD to imply that ROTR is an actual exclusive, to further add fuel to fire.
7. Eurogamer Phil Spencer interview where he explained his position. This was an interview that was referenced by both sides of the camp, those who believe it's a timed exclusive, and those who believe it's a bonafide Xbox-exclusive that will only come to PC later, never PS4. Why was this interview so polarising to that extent?
8. In said interview, Phil defended his purchase of ROTR's exclusivity, making references to Uncharted, etc. He also used terms like "I didn't buy the franchise, I don't own the IP in perpetuity" and compared the deal, calling it "similar" to Ryse/Dead Rising 3, both games that are never coming to PS4, because it was fully funded by MS. He ultimately ended it by saying "the deal has a duration"
So basically, Phil basically admitted it was a timed-exclusive, but used very clever PR-language, referring the Tomb Raider IP (instead of referring to just the game) when talking about the exclusivity deal and saying the deal is 'similar' (similar =/= same) to Dead Rising and Ryse, knowing full well those 2 games are never coming to PS4.
9. In respect to the interview above, Crystal amended its original post, but they said "Phil Spencer confirmed that ROTR is a timed-exclusive."
10. Not too long later, the same post above is amended from "timed-exclusive" to "the deal has a duration."