In 1.410(b)-7©(1), a "plan that consists of elective contributions under a section 401(k) plan, employee and matching contributions under a section 401(m) plan, and contributions OTHER THAN ELECTIVE, EMPLOYEE OR MATCHING CONTRIBUTIONS is treated as three separate plans for purposes of section 410(b)."

Does anyone have thoughts on what the capitalized lang has been interpreted to mean?

The language is trying to communicate that if you have 3 separate "things" in your plan, then you must treat them as 3 separate plans for 410(b). Thing 1 would be deferrals, thing 2 would be the combination of employee after tax contributions and any employer matching contributions and thing 3 is anything that isn't in thing 1 or in thing 2. In most cases, thing 3 just refers to employer contributions, like profit sharing contributions.