First the date: 1 MYA was the time of H. erectus, not the AMH I was referencing. That's fine, but you'll probably be unsatisfied with the evidence from the period because it's notoriously thin. Regardless, by this time our ancestors had shifted to include megafaunal hunting and harder, diverse plant foods in their diet, so H. erectus populations were likely eating both. See [1]. For a good (slightly outdated) overview of the evidence problems, see [2]. In later periods, we can discuss things like dental microwear patterns, archaeobotany, optimal foraging models, and coprolite analysis as the evidentiary bases are so much better.
Secondly, you have to understand the difference between "plants were a large component of the diet" and "carnivores". All the former means is that meat was only about 30-70% of the diet, not upwards of 90%. The exact amount would have varied hugely by group, environment, and even the season or year. The diversity of the plants eaten would also have varied for the same reasons. For instance, some groups in the Mediterranean basin in the later Upper Pleistocene were sedentary foragers who would transition to nomadic hunter-gatherers at other times.
[1] http://doi.org/10.1126/science.1236828
[2] http://doi.org/10.1086/666700
edit: overview of the elements of "forager diets" and the various viewpoints. There's also a large body of literature on archaeobotany, especially from temperate regions.