This doesn't make sense. People are going to forget about this incident in a couple of days, and nothing will change. Why would Russia sacrifice their plane for a couple of days of bad PR for Ukraine?
Someone fucked up and did not tell the air defense crew to hold their fire, most likely. Ukraine says it was the Russians that forgot to tell them. Maybe? You'd think the details of this prisoner exchange would have been hashed out days before in detail, so I'm thinking it more likely someone on Ukraine's side forgot hand down this info to the AD crew. But who knows, it's gonna be he said, she said.
The fact that Ukraine is already is floating conspiracy theories makes me think they're full of shit.