"Happy new year!"
Translation:Boldog új évet!
It's the object of an implied verb "I wish you .... !" and so this conventional phrase takes the accusative case.
Similarly to all the other wishes, like "Jó estét", "Jó éjszakát", "Boldog születésnapot", etc.
Probably because you missed the accent of the Ú.
I don't think langauge courses in general are too keen on teaching abbreviations so early on.
Also it should still be évet.