While this isn’t cheating, it is just a teeny bit anti-social.
Something we know (though I don’t really understand) is that people don’t read the game details especially well at all.
I guess they come looking for, and are accustomed to finding, straight up go games.
So in general we need to take a special effort to warn them that something strange is afoot, when something strange is afoot. Otherwise you will certainly catch people off-guard - even if you didn’t mean to - and they will feel irritated about having their time wasted. Even if that isn’t justified.
That’s why there are all those warning signs etc on the common unusual settings that trip people up. To try to avoid the otherwise inevitable moaning and groaning.
In this case, one extra thing that the “experimenter” could have done to make everyone’s life a little easer is emphasised in the game name what this was all about. It was not a normal “Friendly Match”, it was a silly experiment.
As such, you really do owe it to your opponent, out of courtesy and consideration of not wasting their time, to put - ideally in BOLD - THIS IS AN EXPERIMENT WITH A SMALL BOARD" or similar.
Of course, if you are of the opinion that people should carefully read what they are accepting, and it’s their own silly fault if they accept something strange … that’s up to you: you certainly will get complaints from time to time.
I will also add that if you repeatedly do it, and repeatedly get complaints, we will ask you to stop. This has happened in the past: a person was clearly doing “experiments” mostly to experiment with who they could trick. That got old really quickly.