It has the marks of vertical impact, including the rudder separation, as well as the way the engine separated at the firewall. The aircraft components remained together, with no obvious deformation folding wings or tail back, or indications of a wing rupture near the active fire.
One notion tossed about involves a failure to secure an oil drain plug, but I see nothing to substantiate that at this point, beyond guesswork.
For those making baseless claims, they'd have a little more credibility than zero if they bothered to provide citations. As it is, it's little more than muddying the waters. At this point in absence of anything concrete, the rumor mill is just that.
That canopy is open, as noted before.