casual witnesses

What does "casual witnesses" mean here? Does it mean "witnesses whose job is not to witness that space but they are the users of that space"?

ough it would be a mistake to dismiss the play strain as ‘mere fun’, its focus is ‘self-contained’: towards the interactivity of participants typically engaging publicly in some kind of familiar game, such as playing tig in the Jardin du Luxembourg in Paris, to use one of McGonigal’s examples. Clearly this may still emerge as ‘meaningful spectacle’, on account of its unauthorised commandeering of formalised public space alone, for instance. But, unlike performance, its impulse is probably not to engage at a profound level with a ‘contradictory problematic’ arising specifically from the location in question and directed at an audience of casual witnesses who are, though it is difficult to generalise in this regard, real users of that space with a particular relationship to it. In some circumstances those witnesses can become ‘secondary participants’ if they are drawn into the activity in operation, and this may, of course, occur whether it is play or performance.