After the meal had been finished, Sariputta gave a Dhamma talk to Tambadathika, as was customary, although the mind of the retired executioner was distracted, because he was feeling remorse remembering his former employment, and as a result could not pay attention to the teaching. Sariputta noticed this and asked him if he had killed those people because he wanted to, out of hate or anger, or was it because he was ordered to. Tambadathika replied that he was ordered to kill them by the king and did not feel any hate towards them. Sariputta then reassured him that he did nothing wrong, this calmed Tambadathikas mind down and was then able to focus and listen to the Dhamma.
After the talk he accompanied Sariputta back to the monastery, however, on his return journey home he had an accident and died as a result.
When the Buddha heard of this he remarked that Tambadathika was reborn in Tusita heaven, which raised a question between the mendicants as to how this was possible for someone who killed so many people to be reborn there. The Buddha answered this question with this verse DhpV.100 “Even if one thousand words were spoken in connection to unskilled endeavours.” It would be better to say one word, which having been heard would bring about calm.and if one dies with a peaceful mind, it leads to a good rebirth, although if at the time of death our mind is confused or angry - we face a bad rebirth.
Origin stories do not always focus on every detail, and may ignore details which may seam to need addressing, however, they are making a specific point which sometimes seam like a secondary issue, in this case, if we only read the origin story it seams strange the Buddha ignored the comment of Venerable Sariputta, and the previous employment, yet this wasn't the point of the story, the point was to emphasise the power of a calm mind. For us to get lost in the rest of the details adds on to the reason the story is the way it is.
The origin stories of the Dhammapada are added by Buddhagosa, the 5C commentator, and may or may not be from older sources, however there are other origin stories, mainly found in the vinayapitakas suttavibhangha, which are original and show a similar “strange” ignoring of something which should, one would think, be addressed.
It is well worth remembering that in these cases passages may have been omitted to remain focused on the point trying to be conveyed, or the issue being dealt with, or that the other “issues” may have been covered and talked about, only these were organised in a more appropriate place within the canon.