The document is likely written to have employees who are participants in both plans receive the top heavy in the DC plan. Since this person is not in both plans, this language can't apply to them. Thus they get the DB top heavy minimum. Oops.
401(a)(26) counts all employees like the denominators used in 410(b). So, generally your 410(b) denominators for NHCEs and HCEs combined are used to determine your total "count". That total count is multiplied by 40% (minimum 2 if 2 EEs, maximum required 50). Yes, statutory exclusions apply in generally the same way that they apply under 410(b), like for CBA excludable employees.