Are there attacking units in a non combat showdown?

No, there are not. According to Rule 2171 (RiftJudge FAQ), a unit is only considered an "attacker" or "defender" when there is a showdown involving units from two different players (i.e., a combat).

In a non-combat showdown, the designation of "Attacker" or "Defender" does not apply, and units participating in such a showdown do not have those designations.