In the study they do not count ESL as a foreign language, however it's worth noting that not every state counts it as a foreign language either. In California for example, a high school ELD course does not count for World Language (E) credit, but it instead counts as general elective credit (G).

The terms "foreign language," "world language," and "language other than English" are often used interchangeably even though they are not the same. For example, most schools in California have Spanish classes for both native and non-native speakers. Likewise, it is common to see ASL housed in "foreign language" departments. Truth be told, I just used the term "foreign language" since I thought it would be most recognizable to the reader.

No, it's K-12. Remember that in California students are only required to take two years of a language other than English in high school (and that's only if they're on the A-G track). I teach Spanish and French in a public school in CA and where I work most students take two years and stop. Meanwhile, a lot of districts don't even offer language in middle and elementary school.

Source: ACTFL Foreign Language Enrollment Survey (2017)

Tool: Mapchart.net

EDIT: I didn't calculate the %'s myself. They can be found on page 7 of the source.