If it was targeting the site of a rock concert... The victims are not likely to be Putin's core demographic (though that's without checking if the act(s) that were showing were themselves politically-inclined, either way).
There's a number of reasons to attack such a venue (moralistic religious fundementalists, common street-gang violence against another street-gang's
social "territory", common-or-garden 'protection racket'/corrupt authorities that had been faced with a refusal to comply and need to send a message, ...), but I can't immediately see this having .ue hands behind it.
(Unless it
is a Nationalist-inclined line-up, once we know who was supposed to be performing/what audience it might have had.)
PPE:...oh, look, ninjaed. So "moralistic fundementalists" indeed seems likely. Unless that was just an opportune claim to try to sound particularly relevent.You'd
imagine a False Flag would have inclined towards not overtly using "not our kind of people" (obviously not targeting a load of useful supporters, but not trying to avoid them completely). But I just may not have the right sort of bluff/double-bluff/triple-bluff psychology necessary in arranging such things to send the 'right' sort of message in the 'best' and most 'believable' sort of way.
But, regardless, it'll probably soon be spun in Russian media to reinforce the 'party' message, whether or not anybody even had an inkling of it about to happen (and let it do so, passively or actively).