It sounds like he was not formally evaluated, and therefore did not receive a comprehensive evaluation. I would put in a written request to do so. The eval you request should include not only a complete formal OT eval, but also cognitive and achievement evaluation, in particular because qualifying for an IEP requires documentation of impacts on educational progress. There is no way they could have made a meaningful eligibility determination (yes or no) based on an informal OT screener.
If I were you, I would want to know how his dysgraphia is affecting his written expression, both its quality and fluency, which should involve assessing his oral expression as well, so that one can compare his language expression/output when dysgraphia is not a factor (oral language) to his written expression/output when it is a factor. In assessing the educational impact of dysgraphia, key places to look are
1. writing mechanics: spelling, punctuation, capitalization, handwriting, legibility.
2. writing fluency: speed, length of written products, effort involved in generating age/ability-appropriate products.
3. composition: sentence structure, language, usage, extended writing, forms of writing, organization.
Useful data points that help with developing interventions and accommodations include comparing how he does with writing when provided/not provided with various levels of scaffolding or accommodations (graphic organizers, pre-writing activities, priming the pump, dictation software, typed responses, word prediction software, spell/grammar check, thesaurus functions, supplementary oral responses, etc.)
