I guess this makes me a lazy millennial, but I didn't think anything about what the interns did was so bad, or at least worthy of firing. Yes, it was certainly cringe-worthy that they didn't realize one employee was a vet, hence the need for different shoes, but it's not like they refused to do their jobs or anything like that.
I guess I also am not so eager to jump onto the "kids these days" bandwagon because as a general rule I think the intern system is awful. I'm all for having entry-level positions, but internships (specifically unpaid internships) are the worst and perpetuate the worst kind of class issues, because only those who have outside financial support can afford to do them. If the company isn't going to compensate a person like they're an employee, what should they expect?
I am a firm believer in serendipity- all the random pieces coming together in one wonderful moment, when suddenly you see what their purpose was all along.