No reason for them not to pay out gains. In fact, I think they are required by law to do so if they want to be regulated under mutual fund rules.
However, it's possible that they had some carryover capital losses from the market slide at the end of last year that they were able to use to offset the capital gains.
The second link you provided indicates that they estimated that they would not pay out any capital gains. So I'm not sure why you were surprised when their estimate turned out to be accurate.
Since the value didn't drop today, I don't think they'll pull a hail Mary.
I don't like late-December distributions, and I don't like dealing with estimates. But that is the world we live in, so I try to stay adaptable and do the best with the cards I have been dealt. What I do is do my Roth conversions late in the year once I know what my income situation for the year looks like. And I leave a little bit but not too much room between my calculated income and my target income in order to allow for some mistakes. The amount I leave depends on how certain I am of my income estimate (high this year), the cost/benefit ratio of going over my target (high this year), and opportunities I have to lower my AGI after the ball drops (zero this year).