The “potato-y” taste is definitely from the flour. Since the flour is uncooked (the recipe doesn’t have you make a roux), you end up with that raw flour flavour.
The texture is possibly from the cheese. “American” cheese is the processed stuff, like Velveeta, which melts down easily to a smooth texture. “Real” cheeses, especially cheddars I find, tend to take a bit of work with the mixing to melt down somewhat smooth, but can sometimes end up a little grainy.