You're right, I'm sure Tim Cook gave these special Apple Goons a pep talk before they went there, saying, "Look, I know it's days before the event, but make sure you rough up any homeless people you see, because that will help reinforce our tough image and up our street cred."
Or maybe Apple contracted with some security company with instructions merely to "keep folks from messing with the decorations in the week leading up to the event", and gave them Apple shirts to wear so it'd be evident to police (and/or folks looking to mess with the decorations) why they were there, and the guards took it upon themselves to approach the homeless guy.
If you're hired to "protect this thing right here", and you're standing around all day, you can take the Buckingham Palace guard approach and be quietly hyper vigilant, or you can slack off and maybe get in trouble, or you can try to keep busy and start looking for things that "might be" part of your job - essentially widening the net until you catch something that "needs" doing, so you can report and/or feel like, you've done something. I'd guess these guards fell into the latter category.
You're concerned about the homeless (that's good), and you're assigning motives to Apple. But the two things are not necessarily related. If you get a bad hamburger at McDonalds, its probably not because Ronald McDonald came to your local McD's and gave specific instructions that you should be slighted.