The answer is a complex one. On a level, I think that it can be seen that Congress wanted to slow down the war machine that had dominated the American Presidency after World War II. Truman, Johnson, and Nixon, with Kennedy and Eisenhower to lesser extents, had broad powers that committed the nation to costly and challenging war conditions. In the case of Truman, Johnson, and Nixon, their war efforts did not bring about decisive victory for the United States. Congress sought to slow down this machinery of Executive power for engaging the nation in war through the War Powers Resolution. In so far as equating the Executive Branch's ability to declare and propensity to engage in war, the Resolution can be seen as a type of isolationism, or willingness to embrace a Constitutional position that could avoid military conflict.
However, I think that the issue of isolationism might be secondary to the Constitutional issues at play. The framers of the Constitution endowed Congress with the ability to declare and authorize war. Framer James Wilson expressed as much suggesting that this becomes the essence of the Constitution's principles:
[Checks and Balances/ Congressional power]will not hurry us into war; it is calculated to guard against it. It will not be in the power of a single man, or a single body of men, to involve us in such distress; for the important power of declaring war is vested in the legislature at large.
The War Powers Resolution was an active attempt to reclaim the spirit of legislative power that was at the heart of the checks and balances configuration. The framers understood the challenges of a centralized authority being able to declare war as almost a perpetual state of being. This was echoed in the wars of Truman, Johnson, and Nixon. The War Powers Resolution was motivated to return to this vision of the framers, something that was more clearly evident in its intent than in its actual execution. It might be this element which is more overriding than its isolationist condition.