No need to make a mountain out of a molehill.
If you read the piece, it's just a temp Card mini-camp gig at this point.
Maybe Holt just wants something to do. Or maybe wants to try a slice of coaching to see if he likes it.
As to the speculation that McVay wouldn't hire him? I suspect that McVay is real happy with his current coaching staff and saw no need or point in introducing an unknown factor into the equation. Too many WR's needing development as it is. Would make perfect sense to me, anyway.
What's the big deal? Let Holt enjoy his retirement in any way that he pleases. He's earned it.