I have to agree.
The resume & portfolio shows your experience and gets you the interview. The objective of the interview is to see how you fit with the team. Instead of “lack of experience”, they could/should have said “we found a better fit for the team”. And while frustrating to the candidate, they are under no obligation to further define fit.
I think one of the biggest problems with recent grads is they will take any job even though it could be the wrong job. But then again, I would blame the hiring manager for not weeding out the bad fit. The recent grad may not know any better.