Not dumb, and probably only obvious (not even super) to me. :P Cuz I'm a butt.
Blood cats are more family oriented than many cats, and they often live in the very thick magic, where it's easy to lose track of lots of things and stuff can change overnight and all. Also, plenty of dangers, so the protective mothers tend to bond with their kits through blood, siblings or mates might do the same. Mostly from getting injured, it probably started as an accident. But blood's a powerful substance so it lets them share brainwaves, kinda? Not really telepathy, more a strong empathy, but it would make it easier for Matiir and Samaire to understand each other, and if she offered her blood she'd become family, in a sense, so he wouldn't leave her even if she took the chain off.
That's a really simplistic explanation because I haven't come up with all the details of how or why or when it works, but yeah...
She'd have to ingest his blood, too, for it to go both ways.
I don't know if she'd be aware of this or not, it's probably not a widely known fact and most who know about blood cats assume they got the name from the fact that they won't cross boundaries marked by human blood. But her connection with other spirits or maybe having met some hunters or some such in the past would have informed her, if there were any blood cats near Cathan lands. It is also possible that blood cats aren't the only critters aware of the blood connection thing, so she could have learned about it from a different source entirely. Otherwise, she's perfectly free to be confused, or I can try to make it a little more obvious.
I'm really bad at subtle that isn't too subtle. :P