That is absolutely wrong.
Russian support of al-Assad has always been of importance and I would argue is a key reason to the US calling al-Assad a problem, there was little in it for us where as other dictators we do work with and overlook their method of rule. Similar story with Iran, who we have been calling a problem for a very long time.
The truth is the Islamic State of Iraq and the Levant (and eventually ISIS) used to have a different name in the region, which included fighters operating in Syria and Iraq and many other places; that would be al-Qaeda. US Troops and allied Sunni had al-Qaeda fairly well under control around the 2006 surge, but they were never destroyed and that includes taking out Bin Laden. Those still there in 2010 were fundamentally the same looking for opportunity. It was handed to them in the civil war in Syria and the weakness of Iraq's government (the former not our issue, the latter our direct caused issue.) As early as 2011 who became ISIS in Iraq was successful in getting freed prisoners held by the Iraqi government, successful in recruitment and dealing with older experienced soldiers who at one time were under Saddam. In short they rebuilt their strength just in time to take advantage of these conditions already mentioned. As such were in Syria as well operating not in conjunction with the Free Syrian Army but rather in competition, allowing the civil war to alter into a multiple way civil war. Enough so that these so called "moderates" already agreed to not engage ISIS even with our repeated calls to arm these so called "moderates."
But even before Iraq, by principle ISIS is the product of genocide happening in Syria. There was not enough momentum for the Free Syrian Army in 2012 to topple al-Assad and some of the attacks on these people predate that time frame. Facing al-Assad's intelligence services, military, and violent attacks those in opposition became divided and disenfranchised only to soon thereafter become radicalized and militant. Carrying out operations before 2012. At one time these people turned to the world, were ignored, and embraced the idea of Islamic State independence. That could not by design include "moderates" fighting under the Free Syrian Army banner. Just across the border there were other groups disenfranchised in Iraq, by another problem that from their point of view the US created.
Syria is the real reason for this and it predates 2012. The break point, between the now established ISIS and al-Qaeda, occurred because of what is happening in Syria. And why? ISIS wants something they have always wanted, independence from other factions in the same religion. And there is zero evidence that arming the Free Syrian Army would have prevented ISIS operations in Iraq or Syria. al-Assad already made the bed we are living in, which is why Obama got punked so badly by Putin on Syria. It is so bad now that in some ways you could look at al-Qaeda and ISIS in competition with one another when you would think the synergy between the two would produce world wide attacks. But what we really see are the fruits of two terrible trees. Iraq's government weakness and how well al-Assad has handled dealing with the US. The "moderates" there will drag this multiple way civil war in Syria for years. There is no evidence our arming them alone would speed things up... or undo what al-Assad already did to those that became ISIS.