I think the point is that "He who lives by the sword, dies by the sword" is not coming from a place of judgement, but rather a concern for that person's safety. So Ron Paul was not saying that Chris Kyle "brought it on himself" or that he "deserved" it, which you never personally said I'm just throwing that in there, but rather that he's concerned for these troops and their safety. His later explanation of the tweet makes this clear. He's concerned for the lives of these troops, and thus disagrees with our foreign policy putting them in danger. If he was criticizing anything it was the government's foreign policy.
Paul obviously realized his mistake and tried to sooth it over with his second tweet.
It's clear that his first message was to question Kyle for using his talent and reputation as a shooter as a point of access to counsel troubled veterans.
No way to spin around that.
I don't think Ron Paul thinks he made any mistake. I think he used that phrase the same way Jesus used it, and I think his second tweet, which was really on Facebook but no matter, was simply explaining that fact.
As for the second part of the tweet, he was merely questioning whether using that form of "counsel" was wise, and obviously events proved that it might not have been.