A great honor, and definitely someone deserving of it. It'd be nice to have done it in front of fans, but he's been honored at the Garden fairly recently (within the last 3-4 seasons, I'm pretty sure), and they'll definitely have a "Willie O'Ree Day" when fans are allowed back in the Garden - the article alludes to it.
Unless there is some concern about his age/health so it is happening now? He is not a young man.
That was my exact thought, too. He's 85. Looks good for his age! Obviously we know nothing about his health, but in the "better safe than sorry" category, it makes sense. Plus, Craig Smith will have to change his number...if they did that without announcing the retirement, there would be questions as to why he's changing his number twice. And if they're going to announce the number retirement, may as well have the ceremony, even if the fans won't be there for the first one.