At an internal level of 1, the avatar earned a total of 30exp from hitting and killing a level 1 base class enemy, the avatar was damaged during engagement.

So far this means that the following exp gains happened:

Engage: +10
Kill: +20
Dodge/Block: +0

or

Engage: +15
Kill: +20
Damaged: -5

Either one is plausible because we don't know for sure how the difference of 5 comes into play relative to the unit being hurt or not.