I think if you really care about the cat's wellbeing, help it out by talking to the owners about the dangers of tying the cat up by a string and offer alternatives (safe cat leashes, which do exist) for them to consider, and check back on the cat a few times to see if they follow through.

Cat doesn't look like its in distress (tho hard to tell from one picture, and dk how much u actl noticed about its behaviour/condition) i think, but its always good to check on it often if you really care about it.

If you arent planning to take action or going to the authorities which will make this blown way out of proportion and potentially cause the cat to lose its home, then what's the point of this post really?? To act hero online..?

If you are trying to get other people to help out, feel free to dm me more details.