we had a situation where I outnumbered the defender today

I attacked with my first unit, focused him killed the one defender. Next unit to strike did damage to objective. Focused that.

Had one unit left in the attack with pistol symbol. He cant do anything....no one left to attack. is he focused as well even if he didnt focus to strike?

Yes

An engagement cannot end until all participating units have been focused. Whether they can do anything or not doesn't matter.

Pg 23 of the Rulebook states that you do not stop resolving strikes during battle until every participating unit has a focus token or are removed from the engagement.

The remaining units must focus to strike.