Honestly? I think it's strongly implied that it was entirely about holding potential blackmail material over the Trio for Draco. He spends that entire chapter pointedly smirking at them, making veiled threats and keeping Harry and Hermione nervous that he's going to tell at any minute...the only reason he even knew they were moving Norbert that night was because he went to the hospital wing just to gloat at Ron the same way, then pretended he was there to "borrow a book" when Madame Pomfrey found him (and of course, Charlie's letter to Ron was in the book). So it was his absolute last chance to use his blackmail material against the Trio. Norbert would've been gone the next day, with no way to prove he'd ever been there, or tie the Trio to him - that's why Draco was out trying to catch them in the act.
I've seen the interpretation of Draco being excited at sharing the Norbert secret with the Trio, that he wasn't actually going to rat them out -- I think his being out that night trying to catch them weakens it, but at least it makes some sense by Earth-logic standards. The idea he was selflessly protecting students isn't even the standard-issue Slytherbias, it's pure crack-theory at its finest
I would actually read a crackfic where Draco was that awkward kid from elementary school who didn't get that you avoided him because you didn't like him, and everything Draco did in canon was a misguided attempt to be friends with Harry.