Why did Hagrid have to take Draco malfoy to the hospital wing?

Harry and Hermione, along with Neville and Draco, were given detention from Professor McGonagall for being out of bed at night. Harry and Hermione had been giving Norbert to Charlie Weasley at the top of the tallest tower. They forgot to collect the invisibility cloak and were caught by Filch, who had been tipped off to their whereabouts by Draco.

Draco knew where they'd be after he went to the hospital wing on the pretence of borrowing a book from Ron who had been bitten by Norbert. Draco actually wanted to torment Ron and pretend he was going to tell on him. Ron had to give him a book, unfortunately he picked the one containing his brothers letter that gave Draco all the information he needed.

Neville overheard Draco saying he was going to get Harry in trouble and was caught trying to warn Harry about this.

In the movie, this was changed. Neville wasn't involved and Ron was.

Their detention was to go into the Forbidden Forest to find the injured unicorn.