All that I need to know about the manager's schedule is this.
The manager said on May 14 that he would get back by May 17, and failed to respond by May 25 despite an attempt to follow-up on May 19. If the manager's schedule, workload and working priorities were such that May 17 was unrealistic, then the manager should not have said he would get back on May 17.
What he should or shouldn't be doing with respect to his job is determined by his manager and company - not by the public at large, fortunately.
While the obvious case can be made that someone could have been more professional in this situation (as with almost any situation) - there is very little in terms of expectation set here. No promises of consequence were made, no binding contracts... and for all we know, the behaviour of the applicant in this situation was part of the hiring manager's decision process (whatever that might be)
