The article does not provide the slightest clue about why the researchers believe that this is an alphabetic script, taking into account that they say that it does not resemble other known scripts.

Usually it is assumed that a script is alphabetic instead of being syllabic when the total number of distinct symbols is small, but this is not foolproof, because there are languages with a relatively small number of distinct syllables, like Japanese, so there is an overlap in the number of distinct symbols between alphabetic scripts for languages with a great number of phonemes and syllabic scripts for languages with a small number of syllables.

However, in this case it appears that the total amount of recovered text is quite small, so it would contain a small number of distinct symbols even if the original writing system had a greater number of distinct symbols, which did not happen to be recorded here.

Because the small total number of distinct symbols may be an accident in this case, it would not be enough to prove that this is an alphabetic script.

One should not forget that already since its origin, millennia before this, the Egyptian writing system had contained as a subset a set of symbols equivalent with the later Semitic alphabets, i.e. where each symbol was used for a single consonant.

However the Egyptian writing system has never used its alphabetic subset alone (except sometimes for transcribing foreign names), but together with many other symbols used for writing multiple consonants.

The invention of the Semitic alphabets did not add anything new, but it greatly simplified the Egyptian writing system by deleting all symbols used for multiple consonants and using exclusively the small number of symbols denoting a single consonant.

Because the alphabetic script has been invented by trying to apply the principles of the Egyptian writing to a non-Egyptian language, it could have been inspired by an already existing practice of using the alphabetic subset of the Egyptian writing for the transcription of foreign words.

All the many writing systems that have been invented independently of the Egyptian writing have used symbols denoting either syllables or words. Only the Egyptian writing had the peculiar characteristic of denoting only the consonants of the speech, independently of the vowels, which is what has enabled the development of alphabetic writing systems from it.