@jonny if it feels this close to those convos, maybe "oh hey this was great! Just curious, did it pull from some of the conversations we had on [venue]? Because it reminds me of them!" and seeing where it goes from there. I see your fear but honestly at this point you already have a soft enemy potentially by accident—if you ask them to credit and they do, that's good, and if they don't, well, you already didn't trust them because of this, the only difference would be you'd then know it for sure.