They're pretty similar in terms of appearance and ingredients, but they have different textures. Souffles are super light and airy, made by folding in whipped egg whites which causes the souffle to rise in the oven. Chocolate lava cakes are denser with a molten center. Both have creamy chocolate centers, but the center of a lava cake is denser, like a brownie batter. The center of a souffle is more like a mousse or custard. Souffles are also notoriously finicky and hard to make.