Given Bloomberg's history which is constantly doing things which hurt the homeless and others who are disenfranchised, I can't really buy into it just being a liability issue.
A few months back he decided to push a policy which would require single people to 'prove' they had nowhere to go other than the homeless shelters.
The City Council sued against it, and they won. This is actually Bloomberg reacting to his loss. He reacts like a little bratty baby when he loses.
A quick search on the Internet brings up the scads of past swipes at the homeless and against other low income people.
Keep in mind as well that Bloomberg sees himself as better than the rest of us. Here is a man who bought all elections in his quest to rule. He has had to switch parties constantly. One win was as a Republican, one as a Democrat and one as an Independent.
A short while back, he used his power and money to overturn term limits. The people, that is, the voters, had twice said they wanted term limits. The ballot choice indicated that it would be a limit of 2 terms. There was no choice of 3 terms or even 4. There was no mention of grandfathering this in.
Then, in 2008, he began saying that he needed to stay Mayor, that only he could save the city during its financial crisis. This is the same man who at all earlier times had said, 2 terms, that's what the voters asked for and that's all we get. He went as far as saying this to then Mayor Rudolph Giuliani who wanted an extension of a few months after the events of September 2001 (it was a Mayoral election year). However he's Mike Bloomberg, therefore he should get more time.
He got it overturned. He dillydallyed until there was no way it could be added on as a ballot proposal for the year 2009, then had the city council vote it in. He kept at a distance so he'd seem clean. Meanwhile those who voted for extensions suddenly became elevated in the Bloomberg regime.
Let's take a look at James Vacca a city councilman of the Bronx. He was a nobody, a nothing. Then term limits debate came in and he shot to the top...well, maybe not the top; but, became much more visible.
At the time, Vacca the Clown (as I call him), campaigned feverishly for extending the limits to 3 years. He even had the Al D'Amato moment where he used his mother as the reason to do something, It was along the lines of:
Mother Vacca: You mean I won't be able to vote for Mayor Bloomberg a third time?
Vacca: No Ma, you won't.
Mother Vacca: I don't like that Jimmy, I don't like that at all.
Now it should be noted that Mother Vacca was probably able to vote at the time the issue of term limits had been on the ballot. Councilman Vacca never did say how or if she had voted on the issue, or for that matter how he himself voted on the issue at the time.
Since the vote to extend Vacca is now seen at most Bloomberg conferences, much the way that Christine 'I wanna be the first lesbian Mayor of New York City' Quinn used to be at Bloomberg's ass all the time. Quinn has had to distance herself as she wants desperately to be Mayor and has a 2013 target date.
In 2010, the voters, for a third time voted on term limits and again, voted on a two term limit, which knocked over Bloomberg's law, although both he and several others in the city government managed to snag a third term because the vote came in after they'd been seated.
More on term limits, the 3rd vote: http://www.nytimes.com/2010/11/03/nyregion/03limits.html
The bottom line is that Bloomberg sees himself as a god, and all things must go his way or else. If a vote doesn't go his way, you can be assured that down the road somebody will pay. A policy will be overturned or at least challenged if it was supported by someone who he views as a traitor. So, no, I don't think this latest move by Bloomberg was anything other than him having a tantrum and throwing his bottle at the homeless in reaction to the city council having sued....and won, against him on the matter of the homeless having to 'prove' they had nowhere else to go.