With 'some things' he explicitly means ONLY the emergence of the universe in specific. (I guess he thought about other stuff too but I think he has no evidence or good arguments for them so he let them fall as he is usually a really intelligent and reasonable person).
On what grounds? On none, but I'll have to ask him, I think he just WANTS to believe that not everything can be explained scienifically. Which is a fallacy of Whishful Thinking, isn't it?
If it is a god of the gaps argument, then he has reduced his god to a finite process. That makes his god just one finite process in a univers full of finite processes. Not much of a god. He has become a black box, a place holder for a better explanation.
Of course, that is all god has ever been and as human knowledge has expanded, god has had to evolve to fit within those limits. And as a place holder for better explanations, god have progressively been getting smaller and smaller, and will continue to do so as long as we keep learning.
Also notice your friend only uses god to fill one gap - the one gap he believes is most likely to never be filled. There are many other gaps in his knowledge, so why no god there? Ask him how flat screen tvs work. He probably doesn't know. So why not use god or angels or some other supernatural hobgoblin as an explanation? It is no different. But he knows someone
knows and it is a series of natural, explainable processes. And why should the big bang be any different? Why is everything in the universe explainable by natural processes, with one giant exception?
People used to believe ghosts and spirits and demons - invisible people - did things - caused rain, brought luck, illness, made bountiful crops, fertility, etc. But they gave all that up once they learned how these things really work. But where they do not understand, they still insert invisible people. Perplexing, no? I conclude the human brain is not the awesome thinking machine we like to think it is. It is barely capable and we are talking, hairless monkeys, just smart enough to be a threat to all life on the planet.
His god is a monument to his ignorance. A giant idol of anti-intellect, before which he bows and supplicates himself.
Pathetic. Shameful. A total disgrace. I don't see how he can look at himself in the mirror in the morning.