First, this article keeps switching between calling the visible star a "red giant" and a "red dwarf". It is a giant, not a dwarf. Somebody please fix that.
On to the science: To try to explain how a black hole and a red giant might be in orbit around each other, it seems like first we need to describe the orbit properly. This article says that the mass of the visible star is 2.7 solar masses, while the mass of the black hole is 3.6 solar masses. It describes the orbit of the visible star as "nearly circular", but it is orbiting the center of mass of the pair, not the black hole.
The article talks about black holes getting a "kick" in some direction due to some lack of exact symmetry in their collapse. But, that seems to be a random effect. So, unless there is some theory that shows a particular type of asymmetry always occurs during those supernova events, it seems reasonable that a few might not be unsymmetrical enough to produce much of a "kick".
Or, how about a "capture" scenario for a black hole that was not near the other star when it became a black hole? Getting a nearly perfectly circular orbit with a capture would seem to require a lot of "drag" on the black hole as it and the red giant pass each other. Is the red giants expanded outer layer big enough to cause much drag on a passing black hole? Some stars have generated large and rather dense "shells" of ejected matter over their lifetimes, such as Wolf -Rayet types - maybe there are other types as well. And, the relative velocity between the two might not have been very much to begin with when they tried to "pass" on their original paths.
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