Queso dip question - how does one stay watery even after fridge

Delicious preservatives

and it probably isn't cheese

What they’re selling isn’t a true interpretation of queso.

Got some at Walmart and it was solid (good).

Lots of butter and milk

Our neighbor owns a couple of Mexican restaurants in Houston area in his queso is awesome, so we asked him what the recipe was and it was American Cheese, cheddar cheese, milk, butter, and salt

You might could find answers in the cooking lesson MeridianDog and BigDropper gave on the 5 (five) Mother Sauces.
They wrote:
"1 - Sauce Béchamel (White Sauce)
Béchamel (also called White Sauce) is a milk based sauce (developed in the 17th century, circa 1650) and thickened with a white roux. The sauce is essentially a 50/50 mixture of flour and butter, with the flour cooked (blond roux) over moderate heat, with milk added to complete the sauce. It is a velouté sauce (velvet sauce).   [...]
In a sauce pan, add the flour to melted butter over moderate heat. Cook flour for 3-4 minutes, being careful to not brown the flour. This is blond roux and if brown color is noticed, start the roux over. Add milk to the cooked butter/flour mixture and whisk until the desired consistency is achieved. If properly prepared, the sauce will be velvety smooth and creamy in texture.
Béchamel is the base for other sauces, such as Mornay Sauce, which is Béchamel with [...]."
I'm a true size four, so have not had too much queso in my life; but,  I'm pretty certain the Whole Foods' queso does the same thing.

^^^^^

You can make amazing queso with that stuff. Boil the sodium citrate in small amount of water to dissolve it, add cheese, let melt. I've used shredded mexican cheese or cheddar. I add sauteed onions and jalapeno, cilantro and a dollop of guac after it's in a bowl.

You can make almost any cheese into queso with sodium citrate.