If it’s not a ROM edit then what is it, a SAV edit? RAM hacks? Did he ever elaborate?
As far as I can tell, even fixing the checksums for the files doesn’t fix it as well. I can’t even host either of the event locally.
Reasons why these people cannot be performing SAV edits, at the very least:
1. For the one I taught you, we know the game doesn't let other users receive it, unless they are using the same file.
2. For screenshots of these "hosts" that I've seen, have all been gold background 5*. That cannot be achieved with save hacking. (Dynamax crystal is gold background, but only one star. Event raids can up to 5 stars, but only red background.)
3. Common and rare dens alike, the species "isn't saved in the save". All that is saved is "randroll" (a value from 1 to 100), so no matter how you edit the randroll, you can't force an outside den species to spawn.
Thus, at the very least, what you see are not SAV edits.
Perhaps he doesn't want to say "ROM edits" so that his channel gets penalized, or maybe he is using "RAM edits". With the reasons above, can't see why it's SAV edits (if he claimed so).