[quote=@Ellri]
Decent concept [@SimplyJohn], except for one thing... The Grand Master at the time of the Sacking, Zym, wasn't on Coruscant at the time.

Also, why would the Grand Master be summoning him anyways?
[/quote]
The fact Zym wasn't on Coruscant adds weight to the fact Som was still in meditation. Normally it would be a very short period (one night) between a Padawan finishing the Trials and being promoted, but in Som's case he was having to wait for the Grand Master's return and so his extended stay in the Tranquillity Spire left a far longer window for the Sith attack.

As for why the Grand Master would be summoning him...[indent][quote=The Jedi Path: A Manual for Students of the Force, September 28, 2010]"...If the Padawan passed each of the Trials, they would ascend to a private meditation chamber high in the Tranquillity Spire. Following a night of meditation and reflection, the Padawan was summoned to the Hall of Knighthood where the Grand Master of the Order would raise them to the rank of Knight and sever the Padawan braid."[/quote][/indent]
It might seem a bit excessive that the Grand Master would be promoting every Padawan within the Jedi ranks, but I do have canon to support the backstory (even if it's only [i]Legend[/i] canon now.) :)

If you'd like a more solid in-game reason, with the peace accords with the Sith bringing the war to an end, the Jedi Order were standing down from a war footing and returning to the traditions of the past. As the first peacetime Jedi to be promoted to the rank of Knight following the end of hostilities, Som was going to be promoted by the Grand Master in a ceremony which was to be broadcast across the Republic as a sign that things were returning to normal.

It was all a staged propaganda exercise to help comfort the Republic citizens and get them back to work. :P

Even if this weren't the case and another Master was to preside over Som's promotion, it's unlikely he would've been made aware of this beforehand and so from his point-of-view he was awaiting a summons from the Grand Master, or at least the Grand Master's proxy.