What you have targeted when you Ctrl+T Free Transform is what will be transformed. Could be a layer, A path, A selection, a mask I do not think though it can be a brush. Are you sure your brush is being transformed? Or is you current layer an image of a brush. Transform does not work on your entire document. Image Size does that.
I could not watch the video the the sound drove me nuts and the was no spoken words. There no way I would try to follow that video for that length of time.
I'm not sure what you mean but I think I should clarify. The brush I'm talking about is an image of a brush, not a brush for drawing. I know what you mean about the music in the video. I just muted it and followed it from there. I will try to select the layer and see if that does the trick. Thanks for the response.
At that point in the video the entire bounds of the image is selected because the smart object of the shadow was created with an adjustment layer which has a mask on it. (although that was unnecessary)
When a mask - the large white box on the layer at 10:12 - is created it uses the entire image as its boundary. Then the operator created a smart object without removing that mask. So of course when a transform is applied photoshop takes into account the entire frame as determined by the mask.
The fact that you only see the brush selected with the transform box is not incorrect. Do not change any sizes.
You have apparently missed a step in the production of the shadow file but as i said, that step was not necessary anyway.
If the brush layer is the current target layer and to layer is all transparent except for the brush the bounds and the layers layer bounds would be the bounds of the brush. Which seems to be what you are seeing. Make sure you have the same layer targeted as the tutorial before you use Free transform.