Good point! If we're stretching the definition of "coastal" to include proximity to bodies of water, we could also include cities adjacent to rivers and other lakes as "coastal." Then, we can add Austin, San Antonio, Memphis, Dallas, St. Louis, Salt Lake City, and of course Detroit to the ranks of coastal cities. (Depending on who draws the metro area, Atlanta could also be a coastal city using this definition.)

But that's not the grouping of cities commonly referred to as being "coastal." I obviously know that non-coastal != rural, but that equivalence is frequently used in American discourse. See also: "flyover country", etc.

You forgot to add "Well actually" at the start of your sentence.

Longer than Alaska?

No, I think the original statement is wrong, the Great Lakes coastline that Chicago is on is the longest contiguous coastline in the 48 contiguous states, not the whole US.