But where doubt exists better to report than not.

If nothing else this has to be a learning experience for those involved in managing this type of absence. I get the impression that the absence associated with this accident was not warranted but this can only be determined through a proper investigation. The question needs to be asked how the accident could have been prevented, either by the company implementing suitable controls or by the individual adhering to those controls. Regardless of anything else there's been an absence in excess of 7 days allegedly because of the initial accident.
It's also worth considering if the absence was the result of medical treatment. Was the absence due to an adverse reaction to medication? If so then it can be debated whether this is a reportable absence.

One lesson that does need to be learnt is how such an absence is managed post accident and this includes HR's involvement in the process. A post accident home visit may have been undertaken but was there someone involved who could take a view on the severity of the injury and was alternative work discussed to enable the IP to continue working albeit doing something else?

I'd be inclined to agree with damelfc's view on this. It may be a hard line but, equally, it's important to promote a culture that is firm but fair. The company needs to demonstrate commitment to ensuring the health, safety and wellbeing of it's workforce and as a part of that fair culture challenge people where unfairness is perceived to exist.