It's like someone with sense at Bamco saw the initial press release and was like "wait of course we're doing the Vita one why the hell wouldn't we?" and then a higher up had to correct them.
Keep in mind that the announcement said the game has been expanded quite a bit. The PS4 had something like 120 sidequests while the original had 50. It was explained in the announcement thread.
They've probably considered different options.
- Porting the new content to the Vita. They probably thought the investment wasn't worth it.
- Releasing both versions, the expanded PS4 port and the original Vita game. Which could cause a PR nightmare, trigger refunds and who knows what.
- Announcing the game now only for PS4, be upfront and tell it months in advance. Hope that most of those rabid Vita fans wil buy it anyway because 6 months is a long time and it's hard to be pissed that long.
About the whole thing, I feel it's just as you said. Somebody thought it was a typo since most multiplatform NB games have been released so far. Then somebody else saw the problem and corrected the correction.
Or just an intern having fun lol.