They got pissed that you weren’t as desperate as they thought you were when they rejected everyone else in favor of you, and wanted more info to weed people like you out earlier in the future. Or to pressure you into changing your mind; that would suit their desires equally well, being pressure-able or desperate are basically the same for employers.

At least that’s my assumption. I’ve had similar experiences turning jobs down that I just didn’t want after talking to several people, or hearing more about the job, and they all get upset about it. But they certainly won’t be changing anything, so it’s not like there’s a valid reason to demand an explanation.

Whenever that happens, I just tell them “I’ve explained myself sufficiently, and I don’t work for nor do business with your company. I thus have no compelling reason to continue interacting with you, particularly for something you want me to give you that comes at a time and effort cost to me.” I bid them farewell, and am prepared to block/ignore them if they send me anything else. I chose the phrasing to be direct, and let them know it was a wildly inappropriate ask, while still being reasonably professional. I have never gotten a follow-up after that.