Yes; but playing is not passively staring at the world, nor does it involve a lack of exertion, nor yet again lack of a "passing acquaintance". The point of play is that you can exert yourself without having much hard work of willing it. A child with a new toy is highly engrossed, focused, and certainly not passive nor satisfied with a "passing acquaintance".
I guess I reacted to the screwed-up faces in particular; they looked like they were in pain.
Our problem here is the overloaded nature of the word "play". I do not disagree that children learn through play. But I'm using the word differently in my presentation: I'm using it to refer to activities that you (as an adult) pursue casually, as a way to relax or enjoy yourself. If you play the guitar very well, for instance, you might take an hour in the evening to just "play", singing along, etc. This serves many purposes, and is definitely valuable, well-spent time, but it does not serve to improve your guitar playing. To accomplish that, you'd need to spend some time working on guitar techniques that you are less accomplished at.
You can see my problem, hopefully. Ambiguity in language has been the downfall of more than one well-intentioned presenter!
You have overloaded play in a very specific way in your response; playing an instrument. I'd have preferred it if you'd chosen something else, because I think it introduces a third meaning for play (specific to instruments) apart from both the focused play like that of a child and something an adult pursues casually (which I doubt should be called play).
My hobby (as well as my only form of transport) is motorbikes. I do it for over an hour every day. I'm definitely getting better at it, because of an iterative process of analysis and experimentation. If I just looked at it as a means of transport, I wouldn't be so eager to stretch myself; I'd be content with getting from A to B in a safe and not very efficient manner.
It's completely different to programming, so in some ways it is relaxing; it's certainly highly enjoyable; but it is also simultaneously energizing and tiring. It uses a completely different part of my brain, and gets the adrenaline going.
I think if guitar-playing was my hobby, I'd be focused on improving and having an iterative experimentation / analysis cycle. But if guitar-playing was something I did to make music, perhaps to entertain other people, then the focus is elsewhere. It would no longer be play; it would merely be doing.
What I'm getting at is that play (my definition of it, at least) necessarily implies stretch goals, doing things that you have room to improve at, because without challenge it's boring. What makes it different from work is intrinsic motivation, and hence the lack of a need for application of will.
But you're right in another respect, this is all coming down to a disagreement over the use of words, rather than a disagreement in concepts etc. The start of the presentation just rubbed me the wrong way, and I've made far too much out of this small thing...
I guess I reacted to the screwed-up faces in particular; they looked like they were in pain.