I have a client telling me that a basement wall must be at least 5ft from the ext wall footing. Forgive me as I have never heard of this and don’t have time to look it up now. Is he right?

lol …not true.

He is off by about 5 ft

Basement wall, which I presume is concrete, should be centered on the footing, which is typically 16" to 24". There might be a case where an engineer or architect specifies a wider footing, but that is a rare thing.