My friend's baby had the same "black fibers" in poop a while back, after starting solids (specifically purees). They later found out that it was due to bananas. Baby was fine and showed no signs of discomfort. It went away if baby didn't eat bananas. Apparently this is a pretty common thing when babies eat bananas. You mentioned your child is fully breast fed and you had wine... not too sure of the correlation there but did you have a lot of bananas recently?
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One small glass of wine is fine! Don't worry.