Choosing a foldable 20" bike: Schwinn S2280 vs. Citizen Bike Miami
I think the real difference is the weight: Schwinn 47 lbs, Citizen 32 lbs. That's substantial. If your dad is going to be carrying it much that 15 pound difference will really count. 

My impression is that the Schwinn is compromised to get the low stand-over height, and everything follows from there. That can be important if your dad has limited mobility, but if it's not essential don't buy a bike that adds 15 pounds to get it.

Realistically the rest doesn't add up to much - they're both bottom-of-the-range folding bikes that use cheap components and will probably not last very long (a thousand miles or so). I think you need to be clear what you want the bike for and what you expect from it. If your dad is too heavy or rides too much the bike will fall apart quite quickly. Both bikes will be heavy, unwieldy luggage when folded.

I would be concerned about the wheels on the Schwinn, the "6 spoke" pattern wheels look like a gimmick to me. they might go out of true easily and look hard to fix. But they look pretty. The Schwinn is 7 speed, the Citizen 6 speed, but that's pretty irrelevant as neither bike will cope well with hills or high speeds.

The Schwinn comes with a bag, for the Citizen the bag is $29 extra. If that's important to you, it adds 15% to the price of the Citizen. But I think the Citizen is a (slightly) better bike - they've focused on a basic bike with basic components rather than paying extra for marketing bullet points ("sprung saddle", "pretty wheels"), so they can spend a tiny bit more on slightly better parts.