Wie? Was meinst du, welchen Mann?
The accusative welchen is used here instead of the nominative welcher. So the speaker has in mind the paraphrase "Welchen Mann meinst du?".
{vs}: Genau das meine ich – Renates neuer Zeitvertreib.
In this instance, however, it is the other way round; the nominative neuer is used in place of the accusative neuen. The speaker has in mind the paraphrase "Renates neuer Zeitvertreib meine ich" which is not grammatical.
Both sentences share essentially the same sentence construction, so in the 2nd example, I'm tempted to swap in the accusative neuen and say:
Genau das meine ich – Renates neuen Zeitvertreib.
I wonder what causes this accusative-nominative difference between the two similar sentences?