我感觉两个人说的都没错。

For tax purpose, a single member LLC can either be treated as a disregarded entity and file with owner's personal tax return or be treated as a Corp and file a Corp return.

I might be wrong but in my opinion, it will be easier to treat it as disregarded entity in your case. Since this single member LLC is owned by another partnership, this LLC should be reflected on it's owner's federal tax return as a division of the partnership.

The way your CPA chose was not wrong but not the simplest one.

Just my 2 cents.