WARNING: The following contains major spoilers for Star Wars: The Rise of Kylo Ren #1, from Charles Soule, Will Sliney, Guru-eFX and VC's Travis Lanham, on sale now.
When The Force Awakens first depicted Luke Skywalker and R2-D2 watching the master's Jedi temple burning down, fans were led to believe this was the work of Ben Solo as he turned to the Dark Side of the Force. Rian Johnson's The Last Jedi also suggested just as much with Luke even thinking this was the breaking point into the boy's descent as Kylo Ren.
However, thanks to the first issue of his origin story, The Rise of Kylo Ren, we now find out it wasn't young Ben at all who set fire to the temple, it was a terrorist attack carried out by the Knights of Ren for which the young Jedi shouldered the blame.
This issue opens with the motorcycle gang-esque Knights of Ren in the past, led by Ren and his lightsaber, Ren (yeah... that's a thing apparently), on a recruitment mission which goes awry. They were supposed to leave a crystalline planet with two Force-sensitive additions to the roster but the job's botched and both are killed. When the leader indicates Master (presumably Snoke) will find another potential recruit, he's asked what their next mission is. "Let's go find something to burn," he replies with his sinister mask and scarred body, with the very next page hinting at what arson was committed.
We jump to Ben looking on in horror at the temple burning down with people inside it. Clearly, the regret on his face hints he didn't do this, but seeing as he's so untrustworthy we can't put it past him to have done this and then snap back to his senses, shocked by what he did in his fit of rage. After all, in the Rashomon sequence in TLJ, when he found Luke with the lightsaber over him, Ben displayed enormous power to destroy his hut -- basically embodying a Sith at his angriest point, similar to his grandad, Darth Vader. It stands to reason he'd then purge all connection to the Jedi by attacking the temple and burning the past, as he so eloquently loves putting it.
But when Ben defeats his fellow students and heads off looking guilty, escaping on a vessel to go to Snoke, we finally see his true role in this bombing: He had nothing to do with it at all. Another flashback shows him in the wake of the Luke fight asking, "Why did you do it?" as he stares at the fiery scene. Now, it seems he's asking the spirit of Luke at the temple why would an uncle attack his nephew. When he does so, the skies above turn red and lightning hits the temple at the same time as it blows up, but it's hard to see this being Ben because even as the bitter Kylo he's never displayed such power.
Instead, from Ren's words about starting a fire, it's pretty obvious this was the doing of the Knights. This is backed up by the next scenes in the flashback when Ben yells "No!" and tries to run into the temple to save any survivors. But the flames somehow keep blocking his path and the shockwaves keep throwing him back -- as if someone is manipulating the fire to keep him away from saving anyone.
"I never... I didn't want this," he laments as he looks on petrified. The kicker comes in the response, though, which is seemingly Snoke in his mind. "And you did not choose it, Ben. The Jedi did. Skywalker," it replies, which convinces Ben not to head to his mom, Leia, on Hosnian Prime, but to go to Snoke's secret flowery sanctuary.
What's even more intriguing is while this all seems like dominoes being knocked down to push Ben to Snoke's lair to become Kylo, it may well be an act of revenge against Luke as well. Ben did admit Luke hurt Snoke and maybe even disfigured Ren in the past while battling the Knights, so this could be a two-for-one: revenge by blowing up his students and also, taking Luke's prized pupil in for the ultimate corruption.