Now I'm not saying that our relative had a secret life we didn't know about (she categorically did not), but there were quite a few people at the funeral who didn't say anything at all to me or my sibling either before or afterwards.
At least 2 I knew of (childhood friends of the family) but had never met, were joking with others but didn't acknowledge us as closest relatives. At least 2 more disappeared straight after we came out of the crematorium. I'm sure there were more folk inside than I spoke to outside but in the hubbub just slinked away.
I do admit to doing the same once, recently at a friend's husband's funeral, but there were maybe 100 plus people there lined up to pay condolences, and I messaged later to apologise for not loitering but having been grateful to have been able to pay my respects.
AIBU to think that in a smallish funeral, you at least pause to say a word or two to the bereaved, even if it's by text later?