Baha'u'llah must have mistaken these words as part of the Bab's original text.

In fact, two sections from the Panj sha'n in INBMC 64 more or less equal what we may presume to have been the text of the Lawḥ-i hurúfát. This, in turn, would explain a passage reading: 'What was sent down for his excellency al-Asad, the single, the unique, illumined with the eternal light, the name of God, ad-Dayyán, quoted by Bahá' Alláh in the letters referred to above. This sentence does not appear in the Panj sha'n text, and it is my assumption that it represents a scribal addition placed at the head of the text as distributed independently. Bahá' Alláh, however, as is evident from his use of the preceding phrase qawluhu ta'álá ('His words, exalted be he'), must have mistaken these words as part of the Báb's original text. It is, of course, plausible that the address was added by the Báb himself when the text was prepared for despatch to Khú'í.

(The sources for early Bábí doctrine and history A survey by Denis MacEoin)

https://bahai-library.com/pdf/m/maceoin_sources_babi_history_proofed.pdf