What Can He Tell Them

Please house, I need your suggestion on how to tackle this situation.

A friend works in a manufacturing company but had to resign to join a rival company, after working for like 2years.  Unfortunately, the new company had management problems and wind up barely a year after he joins them.

He got information that his former position is vacant and he applied.  Now, he’s been called for interview in that same post and company, he resigned from.   The problem now is, what can he tell them made him resigned at first? To him then, the motivating factor was just the finance but can he tender that now, won’t it be used against him.

Any idea on how to tackle this situation will be appreciated.