Whether this results in a finding of no eligibility depends on your state statutes, and on your school practices. Most of the scores are generally within expectations for a GT learner, with the exception of the two writing tasks, which are, indeed, age-appropriate without necessarily being ability-appropriate (aka, they can be considered "unexpected underachievement" under some state statutes). A few thoughts:
1. Written Expression is a single subtest made up of a number of writing tasks. Does the write up include any kind of error analysis? This instrument does allow for a reasonable degree of more fine-grained interpretation. If it does not describe error analysis, I would ask them if any patterns were observed when error analysis is conducted. The examiner does not need any special materials outside of the base test kit to do this--though they will do better with interpretation if they have stronger clinical skills. There are qualitative differences between writing that has most of its point deductions taken for mechanical reasons (spelling, capitalization, punctuation), and writing with most deductions in language categories.
2. Handwriting is not the same as written expressive language. This subtest is largely untimed, and consists mostly of brief written responses, with the exception of the final extended writing sample, which does not constitute all that much of the overall score. His products were not penalized for poor handwriting. If it was legible to the examiner (who, if they are anything like most of the assessors I know in special education, myself included, probably can decipher a pretty extreme level of illegible handwriting), then it was scored on his actual work, rather than his handwriting.
A more important question is what accommodations and skill remediation are actually needed. Hard to tell from just these scores how he does with authentic grade-level writing (which is more like the extended writing part of the subtest--which we can't tell if it is consistent with the brief writing samples). If his handwriting is nearly illegible (or maybe not even nearly!), then assistive tech accommodations (under IEP, 504, or building-based general accommodations, such as exist in many 1:1 technology schools) seem appropriate: typed response, standard word processing supports, maybe speech-to-text for first drafts. If that alone brings the quality of his written product up into his ability-range, then he may not need the intensity of an IEP. Possibly a 504 or generally-available accommodations (such as in universal design for learning or 1:1 tech buildings) would be sufficient. If the quality of his writing is still compromised, even after handwriting is fully accommodated, then it makes sense to look at where the actual written expression deficits lie, and discuss additional expressive language supports. These are the types of questions that should be explored in the discussion not only of eligibility, but of appropriate services.
