In fact Buttigieg got as much from liberals as Warren in Iowa (entrance polling, so give or take) and 15 % of the votes from non-whites (though this was most likely a small sample and therefore in no way certain to be representative of a momentum).
Biden's chances does indeed rely on electability, but even among those focused on beating Trump, Buttigieg ended up with more votes. If that ends up representative during the next states, he is lost
It's all one state and one that doesn't represent the country very well demographically, but it has given some interesting pointers for especially Buttigieg. It is still very likely that the lacking support from minorities will be in the way of his chances (and I still don't give him much of a chance), but Iowa has without the slightest bit of doubt been a major boost. He'll need to keep it up in NH and pick up new voters, also outside his demographical base.
But Sanders vs. Bloomberg? I believe that a brokered convention is MUCH more likely than Bloomberg unless some of the moderates withdraw early (after Super Tuesday at the very latest). Even at this rate Biden will be getting way too much delegates for Bloomberg to get the majority.