When you want to say “constituting a tort,” say “tortious,” as in “tortious interference with contract,” and not “tortuous” (unless you’re trying for a pun). The dictionary definition (I quote the Random House here) reports that “tortuous” means “twisting, winding, or crooked,” “not direct or straightforward,” or “deceitfully indirect or morally crooked.” Much tortious behavior may also be tortuous, but the conventional label communicating simply “constituting a tort” is “tortious.”
And some quick Westlaw searches reveal that the dictionary definitions are indeed consistent with legal idiom; “tortious interference,” for instance, appears about 2200 times in American cases from 2008, but “tortuous interference” only about 70 times. (Quickly eyeballing the latter set of cases suggests that they generally do use the term to mean “tortious interference,” and not simply as a reference to interference that happens to be twisting or winding or deceitfully indirect or morally crooked, independently of whether it constitutes a tort.)
I suspect that “tortuous” to mean constituting a tort is rare enough that it would indeed be properly labeled an error, which is to say a departure from standard usage (see Horace). But even if using “tortuous” in this sense isn’t an error, it’s not idiomatic, and is thus likely to be distracting or annoying to many readers. It’s wiser, I think, to use “tortious” instead.