Number 1: Hip hop’s built (to at least as great an extent as EDM) on sampling. And while the degree of respect for clearing and getting authorization to use samples has varied over the years and between artists, as a reference point, Eminem’s breakthrough ‘My Name Is’ uses a Labi Siffre sample as its hook, and Eminem altered the lyrics and content when requested to make changes by Siffre (who is gay, and did not want to be associated with homophobic slurs, for example) in order to get clearance to use it. So there’s evidence there is some basic respect for the artist you’re borrowing from over and above just doing the minimum the law allows or asserting your rights over them. So you know, it might have been nice for Guetta to call and let him know, you know?
2: he’s also part of a culture of musical insults and attacks and rap battle dissing, where throwing out names of other artists and making jokes about them (and worse) is part of the game (see my tongue-in-cheek sibling comment ‘nobody listens to techno’, which is an Eminem lyric about Moby of all people). So he’s more likely to just drop a mean word about David Guetta in a track in the future and call it even than to take him to court. Which would have the advantage of giving Guetta an awesome sample he could drop into future sets, and so the whole cycle completes.