"God" was mind controlling everyone into doing specific choices, making them think they could choose their own reincarnations but in reality choosing for them. The MC realizes once he realizes his friend -- who would be slow and methodical -- jumped to suggest they all reincarnate as their MMORPG characters, despite not knowing that was possible, and that they should all pick a specific castle, despite not knowing anything about the new world including the name of the castle. Which was completely out of character for him.
Furthermore, the MC realized he had picked a stupid race -- Quarter (Half) Angel, which was absurdly expensive and he could have picked "Holy Beastman" or "Dragonnewt" (Elminage references I think heh) instead for the same benefits but less points. And he skipped past "Luck" to take "Faith," which basically is the same thing as "Luck" except it gives him "A Destiny From Heaven" -- i.e., it would have made him a slave to God post-reincarnation. Or just turned him into an Isekai protagonist. And when he realized that, he realized something was trying to hide parts of the UI from his eyes, making it so he couldn't undo things... but he guessed where the cancel button was to undo Faith and take Luck instead.