Note that just because it happens to be a public restaurant in a Muslim instead of a non-Muslim country, it doesn't (necessarily) mean that other restaurant patrons are likely to be paying attention to you at all, much less prevent/protect you from doing anything inappropriate.
What is important in avoiding khulwah is that it's reasonable to expect others to notice and/or intervene so as to keep your interactions within acceptable limits. Chaperoning is the obvious (but not necessarily the only) solution.
It is impossible to just give a general ruling regarding "restaurants in a Muslim country"; there may or may not be public venues in Muslim (or even non-Muslim) countries where social interactions are moderated such that khulwah is not an issue. In my own (non-Muslim) country, even though the moderation is not according to Islamic mores, there is no shortage of moderated social events. I imagine one could find such in a Muslim country as well, but the responsibility is still on you to ensure that it's appropriate.