The answer to your question is provided by Garry and Big Al. The only thing I would add is to better understand Black Powder keep in mind “hits” do not equate to casualties per se, but rather the morale state of the unit.
So as Al noted, by winning the combat, your unit is feeling “euphoric” and so no “Break Test” is required. But it also exhausted and worn and fragile, hence its current Shaken status.
In subsequent turns, the unit could be rallied and its morale status improved (up to one hit only on the unit… that last hit reflects that the unit has suffered some morale impairment that no amount of encouragement by their general can overcome). So the casualties the unit suffered are not suddenly being risen from the dead, but rather the remaining men have recovered their morale after the carnage.
I don’t know if this helps, but it took awhile for me to separate the concept of casualties (not a factor in Black Powder, from morale status which can move up and down).
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