I think part of the problem is that people keep asking the question (of course), so he feels he needs to give them an answer, instead of just saying "I have no idea". Most reporters would not accept that answer and ask futher questions. I think he is just trying to ditch this with giving a timeframe that of course he cannot keep (for whatever reason, we don't know what is happening behind the scenes).
I also think it is mostly due to this Asian habit of "keeping face" in front of western media, who honestly have no clue about X Japan's history most of the time. To these reporters, "this summer" is a good enough response, if he'd say "well we have been working on it for 20 years and I have no clue when it comes out" would probably sound really really awkward to say to a western journalist you try to get to promote you. You want to break into the west, would you admit to Rolling Stone magazine that your album gets postponed every 2 years? Probably not.... Not very smart way to promote you. Back home he is more open about this, see his own yoshikichannel piece where he basically admitted he is fed up with this question. He would never admit that in front of English speaking journalists. I think this is the reason for the discrepancy in his style of communication. He wants to appeal to western jouralists.