A long lens means you’re further away, no one would know what you’re taking a picture of, unless they understand something about photography or are looking directly into your lens. However a crop camera or mirrorless with a prime makes you less visible then if you walk around with a FF with a massive lens attached to it and they might not take it as offensively as they most certainly would If they notice that your taking a picture of them with a pro camera and lens, the latter can really piss them off.
Yes France have quite strict regulation, so you should always ask for permission, especially if you intend to use them online and definitely if you intend to make a profit of it. You can really get into serious trouble if you don’t.
And no means no, so if you have taken a picture and they ask you not to, delete it, even if it’s a winning shot..
Regarding the picture I would probably have blurred the background just a tiny bit more, that would have made the couple stand a bit more out from the background. I would probably also edit the black hair out and the cranes too.