I don't think that's correct. My understanding, at least, is that the gravity cue is far stronger than the light cue, such that a plant will turn away from sunlight to follow gravity. If you think about it, this almost has to be the case, as there are many instances when a plant has to grow without any direct sunlight, e.g. when shaded in the understory, or before the new shoots break ground.
I recall learning that geotropism exerts the stronger influence that phototropism.
I’d put my money on geotropism first.
Plants can detect “up” by sensory cilia at the “bottom” of a cell getting disturbed by pellets that settle out of the cytoplasm.
Geotropism is essential for the young spout to grow UP out of the soil.
Once up out of the soil, a plant uses heliotropism to turn its leaves towards the Sun. It doesn't grow towards the sun, as much as it turns towards the sun; because where the sun is changes during the day. Heliotropism is accomplished by swelling tissues with water, while evacuating other tissue of water- causing the stem to twist, turning the leaves towards the sun; facing East in the morning and west in the evening.
Thanks for the example. When shaded in the understory, many plants and trees will grow horizontally to get out from under a larger plant. Or, out from under a ledge.
And yet, in reality, a plant will ignore gravity, to follow the sunlight.
You can do this test yourself, at home.
Set up a plant so that the only source of light comes from below the level of the planter.