I'm guessing that the mild to moderate question makes the difference between the Vocational Expert deciding whether you can perform sedentary work or no work.

If your claim was solely mental or could be approved solely on the mental claim, than no, the grid rules wouldn't be used. Because you have a combination of disabling conditions, and you were 50+ at the time of your Alleged Onset Date, than yes, the Grid Rules do apply to you. In fact, one of the most common reasons to modify your the Alleged Onset Date is because it becomes easier to qualify at ages 50 and 55.

http://www.disabilitysecrets.com/res...s-are-used-det

"Non-Exertional Impaiments

You may still be able to win your claim if you have non-exertional impairments that limit what you can do, even if your physical RFC is for heavy work or the grids say you aren't disabled. Non-exertional impairments can be those that affect your mental functioning (such as depression), non-strength-related physical limitations (such as problems using your hands or fingers), or environmental limitations (such as not being able to be exposed to smoke, fumes, dust, noise, or temperature extremes). The grids are to be used only as a framework if you also have non-exertional limitations that are so significant that you can't do a wide range of jobs in your RFC level. For more information, see our article on combining exertional and non-exertional impairments to win your claim.

If your limitations are purely non-exertional or mental in nature -- that is, you have no exertional limitations -- the grids are not used at all."