Ask your OH to make a sketch too, peas, it's all material to any potential claim.
Anyone has up to three years to make a claim for personal injury so although it is quite a long time ago, the man is not statute-barred, he's still within his time limit to try to make a claim.
If I can advise you one thing - DON'T enter into any further conversation on the phone or face to face with this couple about their intended claim. The fact that they know you don't have pet insurance doesn't preclude them from making a claim against you personally in respect of the injury the man suffered. Check your household insurance policy carefully, the public liability section may have something there, or discuss it with your household insurance company - and if it does, and you do receive any claim letter, send it straight to the insurance company, don't respond to it in any way. If they are going to make a claim, they shouldn't be discussing it with you personally anyway. Don't have any further discussion with them - or if you must, just say that you know it wasn't your dog. It'll be difficult to prove anyway, it's one couple's story against your version.
If they do send you a letter, and you're not covered by insurance, see a solicitor straight away. Don't have any direct communication with the couple once the letter's been received, it could prejudice the outcome of the claim.
Good luck - let us know how you get on!