I don't think this is true. He explained that we would write a travelogue (that would be published), explore the music scene, visit his aunt and play free shows (where he might receive tips).
The article you linked says: "participation by amateurs in musical, sports, or similar events or contests, if not being paid for participating"
It sounds like he would solidly qualify for that, considering it does not sound like these were shows contracted specifically for pay.
And even if, somehow they suspected that he was in violation of these rules, it does not justify their actions.
No, I don't believe so. This is just done as a courtesy, for the audience to show their appreciation. It isn't even barter because there isn't a deliberate plan to exchange a good for a service. I suppose he could preemptively say, "I plan not to accept any free food or tips," but what good would that do really?
If the customers were paying an entry fee, a cover, then it qualifies as work. And you have to apply for a visa waiver in advance before leaving your country.
He _obviously_ said that he was going to be paid, in tips and food.
No one here is justifying the draconian actions of the border guards. We're merely pointing out that, based upon what he said, any border guard in a bad mood would refuse him entry.
The article you linked says: "participation by amateurs in musical, sports, or similar events or contests, if not being paid for participating"
It sounds like he would solidly qualify for that, considering it does not sound like these were shows contracted specifically for pay.
And even if, somehow they suspected that he was in violation of these rules, it does not justify their actions.