Am I wrong for not getting in to my son for telling his cousins their dad doesn’t want to see them?

I was babysitting my niece and nephew today, and they kept telling my son that his dad (my husband) doesn’t love him because he doesn’t come home every night (he works out of town a lot). They done this all day no matter how many times I told them to stop saying that they continued on until my son snapped on them. My son finally said that the reason there dad hasn’t seen them is because he doesn’t want them. (Their parents are going through a pretty nasty divorce and their dad only wants to see them when it’s inconvenient for their mom). this caused both my niece and nephew to start throwing a tantrum. When my sister got here ti pick her kids up they immediately told her what my son said and she got pissed that I didn’t get onto my son for saying it. I personally haven’t talked about my sisters situation in front of my son but my sister will openly talk about it infront of any and everyone Including my son. Everything he said he has heard from my sister telling me or others
Am I wrong for not getting in to my son for telling his cousins their dad doesn’t want to see them?
Post Opinion