So one way to start a conversation about this is to say 'I know I'm probably being silly, but you don't think X fancies you, do you?' This is a good way of introducing the idea of there being some dynamic without being accusatory, and you can see how it lands, it's also reasonably flattering to him that this lady might fancy him.
Easier to start from there than 'I'm worried you fancy her' even if you do think this. Also, people do occasionally have crushes and fancies and they usually pass. I have had and never done anything remotely dodgy about them, but I do think I wonder from time to time.
I'm all for being alert to new behaviour or obvious signs, but it's not practical or emotionally sensible to start policing people's behaviour as a way of controlling if they have an affair or not, for starters it won't stop them if he has it in his mind to cheat. I do agree that situations can occur, but only if you let them, most sensible people try to get out of that before they start, rather than plunge into them, so if he suggested they go away sharing a room for a music conference, I'd call it then, but meeting up with a colleague and going round her house sounds relatively benign.
I think I'd play my own cards close to my chest at this point, as he may have a crush that will fade away, or you may be insecure myself, I'd say 'have a wonderful time dear' and be very busy, perhaps with your own interesting hobbies and take no notice of what he's up to- I think you will get more signs if there's issues and if it turns out she's a lovely person who is welcoming and there's no issues (which is what happened to me on a couple of occasions when jealousy got the better of me) then you haven't spoiled your own relationship over something that isn't happening anyway.
Others may prefer a much franker and more direct approach!
I have also been in the situation in which my husband was indeed pursued by someone creating situations to get him to help out and get closer and he came to me and said what do I do, so it may be that he's quite keen on the music, you don't know what she's keen on but again, I think no point in upsetting the apple cart right now, it's ok to have a bit of a new passion for a hobby now and again in life, and you can get swept up in it but that doesn't mean he'll cheat if he's not the cheating type of person.