Your high school classmate erred in assuming that the world as it is now, is the same as it was then. It was actually quite different according to the limited number of Biblical passages that provide us with some description of the antediluvian world. No rain, plants "watered" by mists rising from the ground, seasons as we know them not present. Whatever sort of calamity struck to create a global flood changed all that, quite thoroughly.
Some have suggested a large icy comet would have set the world reeling and wobbling, inducing seasonal variation when there was none, greatly increasing the amount of surface water while simultaneously breaking up the "great fountains of the deep," etc.
An external introduction of a great deal of (warm, salty) water combined with a massive impact might make a certain amount of sense, geologically. Not that such a thing would be required for God to destroy the world, but it's human to try to puzzle it through and look for explanations.
Besides, lions were not limited to Africa in ancient times—there is the story of Heracles/Hercules and the Nemean lion, the Lion Gate at Mycenae, the lion as a Persian symbol, etc. There are many species which are limited to one or two continents—they couldn’t all have been in the Garden of Eden.