I have never known a cat, or a toddler, who would not greet one of their own. The greeting may not always be friendly, but always there is acknowledgment. A fellow cat, a fellow toddler, is never ignored.
Watch two toddlers encounter each other in a room of adults. Each child may be oblivious to the other adults, save their own caregivers. Or not. Some children seem quite gregarious, greeting and interacting with everyone in sight, true sanguines. But even the shyer, more reserved toddlers will seek out other toddlers, will want to play, to interact. It's as if there's some deep recognition: another one like me.
In my decade of feral cat watching, I've noticed the same phenomenon amongst my feline neighbors. Let two cats pass one another in yard or alley. They will acknowledge one another. The greeting may be friendly: tails held vertical, at right angles to the body, happy sniffings and rubbings. It may be grisly: backs arched, yowlings and growlings and hissings, a display of force, a statement of territory. Or it may be something in between: an ear twitch, a rump wiggle, a tail flick. There are many gradations, and the language of cats is subtle.
Only humans know to shun their neighbors.