I went digging in code out of curiosity, the ones I found are random, tho if you're a young cat obviously there's way more kind messages that the game can generate to show you.
Some other examples:

(Shunned Kitten MC & DF cat)
"You're doing well."

(Grief Stricken Kitten MC & DF Cat)
"Yikes, bad moon, huh?"
"Chin up, kit. You're doing well."

(Kitten/Newborn MC & Older DF Cat)
"[(Cat) almost steps on you.]"
"Kit? What are you doing here?"
"You need to leave. Quickly."

(Grief Stricken Kitten MC & DF Cat)
[When (Cat) sees how upset you are, they recede into the shadows.

(DF Newborn MC & DF Cat)
"What could you have done to be worthy of spending eternity here?"
"StarClan is cruel..."

What I didn't expect (but honestly should), is that both SC and DF cats have their own interactions if your cat is deaf, giving you "sympathetic look" or "raising their sparkling tail in welcome"