The uplifted base on which the "face" sits is only superficially symmetrical, in my opinion. The notion that the right side is "eroded" is rather presumptive, since there is no evidence of a previous outline that would have completed symmetry with the left side and lower curve. The high-order continuity of the lower left portion of the base indeed triggers the impression of symmetry. But to consider the right edge to have been earlier symmetrical and then eroded into asymmetry (with no evidence for either point) suggests the desired conclusion is probably driving the interpretation.
Indeed, the right side of the image shows evidence consistent with heavy landslides, which if anything extended the outline along the convoluted right and upper edges.
If you use a maximum-aspect bounding box method to infer an axis of symmetry (i.e., enclose the feature in the smallest bounding rectangle oriented with the largest ratio of length to width), signifcant features of the outline fail to line up, such as the discontinuity in the upper left with the suggestion of discontinuity in the upper right.
That has limited utility as the method can only work on certain classes of features; and the intuitive contour-from-shading translation may fail to account for coloration.
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