Yes, it could be just that. We have no proof. It is a theory; but so far as theories go, this one is quite plausible. Stale contacts are still contacts; he may not be the only disgruntled KGB spy. It shows that there is a rumor factory somewhere in the GRU and the factory produced this allegation.
Besides, Russia was already involved in Syria, and the UN and Obama wasn’t saying boo to him with regard to that or the Ukraine.
But Pu needed more. He needed a gradual return to the pre-Maidan status of a respected world power, the lifting of the sanctions, return to G20, and of course keeping its naval base in Syria. From the article:
the Kremlin desperately needed the kind of justification which would generate worldwide attention and full international sympathy and approval for military action
Yet it has absolutely no real evidence behind it, even the circumstantial kind. After all, the apartment bombings had those two FSB guys in Ryazan.