Yes, you need to have a detailed conversation with the client. Plan sponsors say things incorrectly all the time using retirement plan terminology that they do not understand. I still have many a client that refers to their safe harbor non-elective and/or profit sharing in their 401(k) plan as a match.
The only thing that comes to mind for this is quarterly vesting computation periods, for example, you vest 5% for 250+ hours in a quarter rather than 20% for 1000+ hours in a year? Doubt pre-approved plan has specific accommodation, don't know if such a modification would cause it to lose reliance. Regardless, I think you would have to have a 1000 hour annual vesting provision override, so if someone was +250 for only three quarters but still +1000 for the year, they would have to vest 20% rather than 15%. Interesting concept if that's what they're thinking, but have fun administering!