Doesn't really seem like Isekai. I mean, I guess it looks like a KIND of isekai. There's a type where some aspect of another world spills over into ours, like the Devil is a part-timer. This seems to be that so far, that the demons invaded his world in the future. If it was another world, a church wouldn't be treated as a cultural heritage site. Then again, isekai authors never seem to realize all the strange modernisms. There was one that was built on the idea of the mc selling soap, not realizing that much of our ideas of hygiene were the result of advertising and the addition of antibiotics into everything. Author didn't even seem to get what soap actually is, that using so much fat like that should be expensive n the setting, or that we had soap for millenniums. Anyway, yea, that scene would be a dead give away that this takes place in the future(that, plus the fact that a demon was already shown to be in his world in the future at the start) but that's only true if you assume the author thought more about the world setting than how it relates to the mc's powers, which almost never happens in isekai.