Well, a little bit of thought went into it. They saw a person they knew driving a passing car. They then thought, 'Hey, that's Joe Bloggs, I'll wave my stick at them in acknowledgement'
Where the lack of thought (and any risk assessment) came in was about the length of the stick, its arcing radius when waved, and the proximity of what might be hit in the ensuing waving motion, i.e the passing cyclist.
I said mild rebuke, you said telling off. Potato/potarto/tomato/tomarto.
In life we gain experience and learn things. If the old person has got to this point in life without understanding the physics of moving objects and their affect on obejcts in their proximity, then yes, they should be told. How else will they learn?
People in general (not just old people) give little hindsight to their movements. For example Col, how many times have you gone to pass someone in the street/supermarket etc, and they've just turned in front of you without looking? I do them all the time, they're called life-savers, a quick glance over the shoulder before you go. Obviously not as critical in the street, but symptomatic of someone with no spacial awareness, or aforthought to their actions impeding someone else.
I do them all the time, was taught to when I learnt to ride a bike/motorbike/fly/ski/skydive. You are about to go in a certain direction - how about LOOKING to see if it's clear? Same principle with waving a stick IMO.
If you've got to the ripe old age you got to last week without this happening, then you've been lucky.
This is exactly what's happened. The old bloke has not looked at all and just waved the stick. If he had looked, seen the cyclist and still done it, then perhaps a shower of juice from a drinks bottle might have been more appropriate.