The joke is, that the owner had no clue about it's dual-use. But he already suspected that something is wrong with his gardening bot (maybe because of some murders). And now it comes for him.
If a tweet (or similar) makes a statement of fact, either mark it as "satire" in the body or provide the original source link backing up the statement (see rule 6)
Old man: Of course, everything makes sense now!
(The ad on the wrapping shows: 2-in-one: gardening robot AND killer robot).
It's from the German cartoon page https://joscha.com (before: nichtlustig/ not funny).
Is the joke that he tried to kill someone with the bot?
The joke is, that the owner had no clue about it's dual-use. But he already suspected that something is wrong with his gardening bot (maybe because of some murders). And now it comes for him.