If you believe something, that will obviously have consequences on your actions, so there's obviously no inconsistency between the verse you quote and what he said.
Sure there is. They're a Christian, and think any action that causes death directly or indirectly condemns you to hell, and it's not given that you can repent. But scripture says belief in Christ will save your immortal soul, and that God is forgiving and merciful. That is not consistent with OPs views, who puts salvation as a "maybe" if you've caused death. If you find a genuine faith in Christ after the fact, you will be saved.
But scripture also says that many people will believe that they are holy and will be saved, and won't be, and this is one of Jesus's parables.
So it's far from clear. People who believe will have works, this is also something with scriptural support. So if you are doing harm, such as by killing people, you probably don't.