I feel like I've seen this beginning 20 times.
I mean, from my perspective it's ok to rip off another manga's beginning as long as you:
A) Change parts of it so details unique to this story will be used later to build the world.
B) Make a parody or make fun of this generic ass beginning.
C) Not dedicate a whole fuckin chapter to this shit.
I mean the author probably knows that he's just recycling the isekai setting since he doesn't have the MC spew exposition.
So he probably knows that he's ripping off the beginning, so why not have it implied like the mechanics of the world!