They both mean the same thing really, but they are trying to teach word order. Compare these two -
"It's a beautiful day today" - He lā nani ia i kēia lā.
He lā nani - A beautiful day / ia -it / i kēia lā. - today
"Today is a beautiful day" - He lā nani kēia lā.
He lā nani - A beautiful day / kēia lā. - today
Yeah if you translate from English to Hawaiian it makes sense, same as Māori word order is important, but that is not the case in English to these extremes, so I don't get why I would have to learn this one phrase in English when I learn Hawaiian. This day today is beautiful. Today is a beautiful day. Same thing in English, I get it's not in Hawaiian, but I'm here for learning Hawaiian as an English speaker not the other way around.