Your screenshot only is showing the first line of the expressions unless that's all there are. The expression on your Audio Amplitude layer is changing the value of the slider so that it limits only goes between 100 and 110. The other expression on the heart layer simply ties the adjusted value of the scale to the slider value. The result of animating the x and y scale of a layer when there's no frame of reference or background is that the layer has the same appearance as zooming in and out. In the tutorial he has some trees on a layer above the shot that do not scale so the background appears to be pumping. In your project there is no reference background.
I believe I put up an example in your question about motion tile using a grid background. You need something in the background that has some detail to make the heart look like it's beating and you are not just animating the scale. If you want to animate scale differently for X and Y you have to separate the values in an array. Using your example I would do something like this for the bottom expression.
s = thisComp.layer("audio Amplitude").effect("Slider Control")("Slider");
[s * 2 , s* 1]
This would scale the heart from 200% to 220% in X and 100% and 110% in Y, but it would still look like you were zooming in and out without some kind of detail in the background.
To simulate a beating heart I'd try the bulge effect instead. Change the top expression to
linear(value, 23, 50, 0, 1)
Actually, I'd remove the expression from the slider so you can actually see what's going on with the slider and make some judgement calls and I'd apply this expression to the Bulge Height
v = linear(thisComp.layer("audio Amplitude").effect("Slider Control")("Slider"), 23, 50, 0, 1);
Adjust the Bulge Center and width and height to get a heart that looks like it's beating without the need for a background with some detail in it. Then just apply motion tile to your heart layer and you're done. Your grid of hearts should look like they are beating instead of zooming in and out.
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