This sounds like a guy who's convinced of his own salvation. The Bible says that Jesus is the Judge, not individual men.
This is a guy who takes very seriously the admonition to "...work out your salvation with fear & trembling".
IOW - Piper is a "leaner". To wit:
"I can do all things THROUGH CHRIST who strengthens me."
"If anyone serves, he should do it with the strength God provides,"
The Bible says that Jesus is the Judge, not individual men.
I think every right-minded person would agree with this - I'm not sure of your point.
Please be careful that you are not more interested in holding onto an opinion - than discovering what is true (hence my tagline 8^)