tbh, I think the detail of whether or not you were holding the lead is a misnomer. If the other dog is allowed to run up to you and yours then even if you had hold of the lead, you still are unlikely to be able to respond quicker than a dog.
To allow your dog to approach anyone without checking it is ok first is naive. Mistakes happen and most of us have had or seen a recall fail so I tend to be understanding etc when it happens with other dogs and is clearly an error, but I also don't think it's on to just assume an off lead/under control dog must be friendly and fair game to be approached.
There are plenty of reasons why a dog might be off lead but not want to be approached. Training and recovery from surgery for two. A friendly out of control dog could be a considerable threat to a dog recovering from surgery so the idea that only aggressive dog owners must take precautions is daft. A few months ago a rescue king charles in my village, who was well on her way to recovering from hip surgery, was bounced on by a failed-recall labradoodle. It cracked her hips back open and set her recovery back 12 weeks. She is also now very reactive to similar dogs because she associates them with the pain of the injury. Her owner is not to blame. The dick wad owner is, for letting their 'friendly' dog approach her because she was off lead (walking to heel) so assumed she was fair game.
Just plain old not wanting to be bothered by someone else's dog is also a reasonable reason, imo.
Dogs are living creatures with minds of their own. Yes, training and good observation means you will be better at predicting how your own dog and the other dog will behave but this is not foolproof and a simple search of google images of dogs and children will reveal how useless most people are at reading dog body language.
If you let yours interact (either deliberately or through failed recall) with an unknown dog without checking first then you are deciding to take a risk. No point complaining when the risk doesn't pay off. You are also forcing the other owner to take the risk as well, whether they want to or not.
Oh, and fwiw, our JRT has been on the receiving end of a vicious attack (in the street, her on lead, the other dog off lead, 50% of her body skinned, £2000+ bills and a 50/50 chance of survival, police involved, other owner severally injured trying to get his dog off her). The other dog was not put down, the other owner was not charged with anything and not liable for vets bills, despite deliberately leaving his dog off lead. The law on dog/dog attacks (service dogs excepted) is not as quoted by pp.