That's a lot of damage against a reinforced concrete structure for an anti-air weapon. I think it's at least as likely to be an impact from an air-to-surface weapon, which would also have solid propellent. The flight profile looks much more consistent with a helicopter or fixed-wing aircraft launch than a surface-to-air launch (especially since, as you mentioned, it's clearly in the early-ish stages of flight). A Buk launch could be vaguely plausible (the Strela series has VERY small warheads), but I don't see the S-300 having that kind of failure mode early in flight.

As you said though, the full picture will come out later. Hopefully they'll find some identifiable weapon fragments eventually.