I don't understand the structure of this... Kia should be "what kind", "what type", right? For instance, "what kind of couple is that?" = "kia paro estas tiu?", so for me it would only make sense that "kia bela paro" means "what a beautiful type of couple" - the kind of couple is beautiful, not necessarily the couple itself (though the first might imply the latter). On the other hand, I wouldn't know exactly how to say "what a lovely couple" --- "kio bela paro!"? I'm super confused =(
It's an emphatic kind of what, not one fulfilling a questioning purpose.
It's like the English:
"What a load of rubbish!"
"What a beautiful poem!"
"What a stupid thing to say!"
The clauses above aren't interrogatives (questions) even though they're headed by the interrogative pronoun (what ). They're declarative statements, where what places emphasises on whatever follows.