There’s no reason that guilt would be absent from helpinghelp a specific person in need (like your struggling mother example). Plenty of people feel guilty taking handouts and will outright refuse help when they might need it.
As for the drive thru thing, I think you might be talking about something different than what I’ve seen/done, which is just paying for your own meal and the people behind you. There isn’t any expectation for them to continue some chain, and in many ways it’s a bit of an empty gesture (they are just taking that first person’s goodwill and passing it to the next in line).
My interpretation of paying it forward is the premise of receiving something when you’re in need, then, when you’re able, to give something back. Not to the one who helped you, as that would be repaying a debt.
I mean, he was speaking at the Black Conservative Federation. It’s sorta relevant just given the venue.