It seems to be a creative choice. Support also comes from Moon sextile Jupiter in Aries, indicative of a generous willingness to share her emotional experiences in a new field. Mark is an Aquarian Sun, which conjuncts Mars and Mercury in the 10th house, and his Moon is in Aries, which, like his Mother's Moon, is on the Ascendant. He has many signatures of a strong-minded, willful, and independent spirit. With an Aries Moon, he cherishes and aggressively protects his independence.
Emotional responses are spontaneous, uncomplicated, unconsidered, and hard to explain.
His emotions may change so fast that he may not remember his old mood long enough to make sense of it for himself, or be able to explain it to his mother. With a Moon-Pluto opposition, Mark can experience his mother as a tricky manipulator. He's called her a control freak more than a few times. With her Virgo Sun conjunct Saturn and a Mars-Pluto conjunction in the 4th house, Mark's impressions are confirmed in her chart. However, because of astrology, Caroline is aware of this particular pitfall and attempts to stay above-board and continue to work on it.