General question first:
In the deaf community, is it considered polite to interrupt two strangers' conversation to correct an incorrect sign?
Background second

:
DH and I use American Sign Language with our infant and toddler, expecting them to continue it as an additional language in the future. I lived with deaf people many years ago and didn't learn nearly as much as I should have, and DH had no exposure before this parenting adventure.
Last fall we were at a petting farm and DH was with our toddler (20 months) in the barn separate from the baby and me. He and DS were talking about the animals and using the accompanying signs they knew. A woman near them broke into their conversation to tell DH he was holding his hand wrong, then added that she uses sign language with kids at her work (she wasn't obviously hearing impaired herself).
My interpretation was that this was no more appropriate than if she'd interrupted to correct his pronuncation of an English word. I admit I'm colored in my view, as I get irritated when I see/hear dads being treated/referred to as inferior parents who need a mom's help. But I don't know if she would have done the same thing with another mom, or if it was even her way of reaching out to start a friendly conversation.
I shared this story recently wtih someone who is not hearing impaired but spends time in the deaf community. She argued that it's normal to correct others' signs in that culture (which I understand). I don't think that extends to other people's conversations, but she thought that it being a third-party conversation was irrelevant and therefore the interruption was entirely appropriate.
Does anyone have more information for me?
Thanks.