Here's an example from Brisbane Times,
"What we do know is the world is more indebted now than it was before the financial crisis." That being so, financial markets are seemingly willing to disregard the flashpoints building up.
It is a set phrase meaning:
- accordingly, as a consequence, as a matter of course, as a result, as matters stand.
(The Free Dictionary)
In the context of the excerpt provided, "That being so" could be substituted for "Assuming that to be the case".
In my interpretation, rather than affirming the preceding quoted statement, "That being so" is used to convey the author's perceived paradox that financial markets aren't as concerned about debt levels as he believes they should be, viz either:
However, the qualification "the flashpoints building up" suggests that the author believes the first point to be correct, and may be implying that markets will fall or correct in future.