I actually don't think anyone even heard Naruto say "Dad." Sakura was really the only one within earshot if Naruto used his normal voice cuz all the other shinobi were in front of him, getting ready to protect him from the Juubi's giant TBB by making earth walls and stuff and i'm sure he didn't yell it, he may have even said it under his breath. after Naruto says "you're right on time, dad" the VERY NEXT thing to happen is that Sakura says "who's that?" and I don't think anyone even noticed Minato until after that.
and it's actually not surprising that the other Kage and stuff would know Naruto was Minato's son. afterall, such information gathering is commonplace and very necessary. it's true that Hiruzen said he tried to keep it a secret, but all the then-Jonin's and those higher up and who were older knew. Kakashi certainly knew and i'm sure that all the ANBU knew... it was really the younger people and citizens who didn't know. I mean if you think about it, plenty of ninja knew Kushina was pregnant and that she would soon be having a baby. Then, both Kushina and Minato die, but there's suddenly a new baby in the village who is an orphan, and looks exactly like minato who died on the day of the baby's birth.... I mean... anyone who knew Kushina and/or Minato probably knew that Naruto was Minato's son, but everyone stayed tight-lipped about it. But with so many people knowing, all it takes is the capture and/or interrogation of ONE of them and in the course of such information gathering, someone like that--especially since there wasn't a curse on their tongue like Danzo put on the root members to paralyze/kill anyone who spoke about it--could easily give up that little piece of info.
So, I was never surprised that other people knew. Afterall, "other" people knew from the beginning. also there was ONE MORE KEY PERSON WHO KNEW--and that was OBITO. therefore it wouldn't be a stretch to think ALL of the Akatsuki knew, and plus it wouldn't be unthinkable for him to spread that info around into the other villages while he disguised himself as someone else or something like that. so I really don't think it's unfathomable for others to have known about Naruto's origin.
and anyways, like I said, all the older shinobi in Konoha must have known... Kushina, pregnant, her and Minato die.. there's suddenly a new orphan who looks EXACTLY like Minato who is born on the day of their death.. they knew. Hiruzen just had everyone keep quiet about it so their ENEMIES wouldn't find out.. or more specifically, Minato's enemies, but of course enemies in general (as minato's enemies were konoha's enemies).
so... I mean of course I could be wrong, but in this instance I don't think so. I was never surprised that others knew, and when naruto said to raikage "blah blah blah my parents!" and raikage responded "yondaime and Uzumaki Kushina..." rather than be surprised, that only confirmed it for me..