To bring some law into this, rather than all the "harden up" comments, I have copied the following from the WorkCover (NSW) website:
A primary duty of care is owed by [an employer] when it:
- directs or influences work carried out by a worker
- engages or causes to engage a worker to carry out work (including through subcontracting)
- has management or control of a workplace.
The [employer] must meet its obligations, so far as is reasonably practicable, to provide a safe and healthy workplace for workers or other persons by ensuring:
- safe systems of work
- a safe work environment
- ...
- adequate information, training, instruction and supervision is given
Basically, this guy has a reasonable case if he can demonstrate that practicable and safer alternatives were available and that he wasn't provided adequate training. Now all the "harden up" people are going to say that you shouldn't need training for lifting a 16kg bag, but the lower back is generally not particularly strong and using the wrong lifting technique can cause damage. Now, if he was given training on the proper way to lift, then it may be more difficult to prove damages.
I would be honestly amazed if he never received any lifting guidance - in this day and age of lawsuits, almost every employer has a compulsory H&S induction, including lifting techniques. I'm an engineer and will likely never lift anything heavier than a pad of paper in my career, but I still had the training.