This rare type of 'Pensive Bodhisattva' originates in the Gandharan region during the Kushan period and is of extraordinary significance for further stylistic and iconographic developments throughout Asia, culminating in the iconographic type of a seated Maitreya in Korea and Japan by the 7th century.
In the Gandharan context, historical scenes of the 'Pensive Bodhisattva' generally represent Prince Siddhartha at his First Meditation on life's sorrows. Indian texts relate this episode from Buddha's life, stating that the young Prince Siddhartha was present at the annual ploughing ceremony officiated by his father, as related by Junghee Lee: "During the ceremony Siddhartha began to reflect on how hard and hateful the work was for the bull pulling the plough and for the farmer driving the bull. Then too the prince noticed how the insects flushed out by the plough were quickly eaten by birds, while larger birds ate the smaller. Filled with pity for the difficulty and misery all living creatures experience, Siddhartha began spontaneously to meditate sitting in the shade of a jambu tree, and felt ecstasy in a trance. Throughout the day he sat motionless in the First Meditation while, as the sun moved, the tree's shadow remained over him. When his father found him late in the day, he realized that a miracle had taken place and dismounted from his horse to offer worship to his son." From 'The Origins and Development of the Pensive Bodhisattva Images of Asia,' Artibus Asiae, vol. LIII, 3/4 (1993), p. 312f. and fig. 1. As a free-standing sculpture, in a slanting leg pose, the Bodhisattva generally holds a lotus bud, identifying him as a Padmapani; compare with the example at the Matsuoka Museum of Art, see I. Kurita, Gandharan Art, 1990, vol. II, cat. no. 151. In the Swat Valley context, he may be part of the Maitreya triad.
For a further discussion based on an example of a Pensive Avalokiteshvara from Mathura, see M. Lerner, The Flame and the Lotus, 1984, pp. 30-35, where the author argues for a prerequisite of this iconographic type in the ancient Gandharan region, as the pensive figures invariably wear sandals, a late Hellenistic influence otherwise uncommon in Mathuran sculpture.