What's all that about?
What is the meaning or purpose of the topic being discussed? A: "Jeff is still really mad at Jen." B: "Yeah, what's all that about? I thought they were best friends." Cross-country skiing perplexes me. I can understand the appeal of regular skiing, but skiing uphill? What's all that about?
what’s all ˈthis/ˈthat (...)?
why is this/that happening?: What’s all this I hear about you wanting to leave?