the results will reflect all webpages that have "all" of those words in the title tag
What are you basing this on?
Everything I've ever seen agrees with you that the results returned will have all the provided terms in the title. Nobody mentions a promise that it'll be all of them.
Also remember that search engines don't only do what you explicitly tell them to. There's all sorts helpful(usually) stuff like spelling correction that's done more or less transparently, as well as customization/localization, eg. I get about twice as many results for your first example.
Keeping in mind that Google does in many cases try to "understand" what you're searching for and act upon that, I can suggest one bit of speculation that seems reasonable:
It's important to note that with this particular situation your search terms aren't arbitrary pieces you can shuffle around without semantic effect. If I search for "restaurants thai" it's possible that I'm just looking for those two words, with no particular context intended. On the other hand, in a search for "thai restaurants" it's much more likely that I am in fact looking for a Thai restaurant. If–remember: speculation–Google does have something like this in place, then it could be used to filter the results with the intent of trying harder to find you actual restaurants(or information on them), rather than pages that just happen to have the terms.
I suspect that if you were to pick another set of terms that were more easily re-arranged without affecting meaning, the difference in result counts would be lower.
