You have a point (sort of). In music, when a band like the Grateful Dead or Pearl Jam say it's okay for fans to record and distribute their concerts, the term bootleg takes on a different meaning. While the recordings may have been done without the express permission of the band, the band does tacitly approve of them. However, they never say that it's okay to sell them.
If someone were to make a copy of one of these band's official releases and then sell them, that would be a bootleg in the traditional sense and you can be sure that the band(s) would not be okay with that.
Bootleg usually means to copy something without explicit or tacit permission and then sell it, so since 20 Tanks was a copy of someone's work (in terms of copying the original layout), but was done with permission of the author, I guess that it's sort of a half-bootleg. Had Red done this without any permission, then yeah, it would be a bootleg.