I am someone who hates attention (to myself or someone with me) that creates a "scene" anywhere. I seem to have spent my life "putting out fires" created by others.
That being said, there are times when a degree of tact is often required, which might jeopardize your "silent" diagnosis. Of course, you two really should have discussed what to do if you were on the verge (or in) a meltdown. You should have plan(s) in place depending on the severity of the situation, including what to do/not do, and what to say/not say. If you haven't done this already, I suggest you do it -- either once, or on a situational-based level.
While meltdowns are common for many of us, they are NOT common for the majority of diners and servers who were witnessing it. Sometimes, when someone is 'in charge,' (such as your partner) it's up to them to "put out the fire" that is blazing around you.
Humans will often be far more understanding of difficult situations if they have the information needed to process the event. So, by your partner 'outing' you (which you didn't want) -- you may have been treated far better than someone who was hauled off by Police for making a scene.
If you have an issue, I'd speak with the restaurant owner (alone, and businesslike, not just catching a bit to eat). Explain your situation, apologize for what happened, and mention that you'd appreciate if he kept that information confidential. That way, he'll know how to react if it happens again at his establishment and he won't have a need to disclose to anyone else.
You can't "deny" anything about you -- especially if it is going to have an impact on how you act (or react) in public. It's fine when no one is around, but when there is a witness or crowd, people need facts.
For instance, if the Police were called, you (or your partner) would most likely have to explain to them what had happened. In the United States, drivers have access to special cards to hand police in case of an emergency. They vary in their wording, but I've included one.
You should also wear a medical alert bracelet that is backed up to a computer with all your information; if you had been transferred to the Police Station or a Hospital, they would need to know about your diagnosis, as well.
If there is anything about you that you don't want your partner to disclose, you need to have an open, honest, discussion. What would need to happen though (if it were me and you) is that you would have to give me SPECIFIC things to do -- and how to answer questions.
I've witnessed situations where I was torn between getting involved and letting the store handle it, until a parent (or someone else) 'took over,' briefly explained the situation, and dispersed the crowd. "Briefly," would include, "It's ok, he's autistic; we've got it covered."
If your diagnosis can cause you to lose your job, you need to figure all this out together BEFORE you venture out ANYWHERE that a meltdown or other event is even POSSIBLE.
Sometimes, the rights of others outweigh your rights of personal disclosure -- especially if it will keep you out of jail.