I guarantee your kitty will be happier in his home than in a kennel. If you trust your friend it’s slam dunk. I wouldn’t let the cat out while you’re gone. If he gets outside he may go looking for you.
I wanted post “laugh” but “insightful” outweighed the laugh. I live with these knuckleheads. Said with affection. There’s a FB post that explains how COVID escaped the lab. They had cat. ;)
Don’t return her. They surrendered her by their neglect and silence. They’re irritated because they think you have their property, yet they treated as just another thing to be tossed aside. They’ve lost their rights to her. Don’t hesitate to bring up the trespassing if they push the matter.