Not RTFT but have read all of OP's posts, and I agree, it's weird, but not uncommon.
My PILs were furious that my SIL and her family got a dog, and all we heard for months was an awfully behaved, dangerous, slavering beast it was, and how their grandchildren weren't safe around it. DDog is in fact a loving, beautifully behaved and very well-trained poodle mix. They did stop visiting for a while, and only when SIL stood her ground and refused to "get rid of it" did they come back - but now refuse to be left alone with it.
Oddly, although they're "dog people" themselves, and loathe cats, they did not seem very bothered by us getting a cat. They don't like him, and don't want him too close, but it hasn't stopped them visiting, and they haven't asked us to "get rid of him."
Also, my BF's parents were horrified that she got a cat. Apparently they didn't think she was responsible enough to look after one. BF is in her 40s, has had cats most of her life, and takes very good care of her disabled child....
It makes no sense to me, but you're not alone!