I mean, harem is a form of poly. Any harem game is a poly game. Me saying poly didn't mean that the girls are also in relationships with each other. There are a couple of lines that indicate sapphic content and/or threesomes might be a possibility at some point, but as of chapter 8 it hasn't happened (I haven't played through ch 9 yet). Rather, I emphasized the poly because it doesn't quite follow the standard "harem game" format.
There's not a clearly defined group of women you are dating who all live their lives in proximity with you as you progress all of their stories. Rather, a number of characters drift in and out and back into your life as events and circumstances dictate. Often you have the option to have romantic and/or sexual entanglements with them. No one seems to care too much if you are doing so with multiple people. And it's left unstated whether the women in question are doing the same or not.
As someone who is poly IRL, it feels like a more realistic depiction of one form of what poly can look like than the vast majority of harem games do (the only one I can think of that competes on that front is Out of Touch, but that's a very different form of poly).