Can only be considered true if you only talk about the game engine. The combat system and travelling are quite the same.
MM2 is much bigger, has more graphics, more monsters, more items, more and slightly changed classes, more levels, more spells, automap, hirelings, ...
You can import your MM1 party into MM2 and you'll see some game engine similarities, but they are different games. They have different stories, quests, worlds to explore, ... .