The source employs «الألمعي» for a person of penetrating intelligence who grasps a matter from subtle indications. A poetic description unfolds what that intelligence amounts to.
الْأَلْمَعِيُّ الَّذِي يَظُنُّ بِكَ الظَّنَّ — كَأَنْ قَدْ رَأَى وَقَدْ سَمِعَا
The perceptive person judges you as though he had himself seen and heard the matter.
The word «الألمعي» has meaning by itself. The relative description gives that meaning vivid content. Its main contribution is uncovering and illustrating the quality, not simply naming an arbitrary new class.