Wondering If someone might be able to give me some clarification on the following situation - I was watching a 10th discussion video the other day and they were debating the situation and there consensus surprised me - I'll do my best to describe the situation, hopefully it makes sense

1. My opponent has set up a screen of 2 unit back to back - I charge the front unit with two units of mine own.

2. My first unit fights and kills my opponents first unit.

3. I pile in 3 inches putting my second unit in bases to base contact with there second unit

They are saying because my second unit hadn't fought and is now in base to base contact it can now fight my opponents second unit which kind of blew my mind

Is this correct or have they gotten it wrong?