Sorry I'm confusing you with the relevant USSC precedent.
Let's examine the issue in reverse. We have a first amendment right to free speech which protects us from governmental restrictions. Tinker stated that schools needed a specific objective in order to restrict the speech of students, that they couldn't do it simply to restrict uncomfortable conversations (Vietnam war protest armbands in that specific case).
If the schools actions didn't lie on the spectrum of a law there would've been nothing that the USSC could've ruled violated the first amendment.
I'm not sure that I can trust your (superficial)... let's call it, "analysis," given that your posts seem to suggest that you don't know what laws are or even the distinction between something "having the force of law" and something being within the "spectrum" of a first amendment restrictive action, rule or policy.
There's also a difference between a "specific objective" and a "specific showing of constitutionally valid reasons" in speech restriction, which is what was actually stated. Under your misinterpretation clearly the bless you prohibition is fine.
Since it was the latter, they obviously had to continue on and talk about what would be constitutionally valid. If you read a little further - i mean this shit is freely available online - you'll arrive at the actual rule: A prohibition against expression of opinion, without any evidence that the rule is necessary to avoid substantial interference with school discipline or the rights of others, is not permissible.
You are so sure that it's violative and you seem to know less about a case I spent 5 minutes researching while drinking my morning coffee.
Is a courtesy "bless you" an expression of opinion? No? Okay, then it must be the subsequent argument with the teacher? Should those be protected?