Problem after oil line is flushed

Went for my 3000 mi oil change at one of those drive thru places 2 days ago. I have a Chevy Suburban with 185,000 miles. They suggested and performed a flush because they told me my oil was clean but there was sludge when they drained it. I want to see if your reaction is the same as the mechanic that I saw today when my car began ticking, the oil pressure light came on and the pressure dropped to zero. They said that you NEVER flush the oil in a car with that many miles unless you know the maintenance history and that it has been flushed regularly throughout its lifetime. I have 2 other friends who are mechanics who told me the same thing.
The oil pump is shot and most likely the crank shaft, bearings, pick up line (all terms I learned today). Is this correct? That a flush should not have been performed. The truck was running just fine. The oil change place said "they've never had this issue before, that they don't actually flush the system but add an additive, and that there are no warnings on the label that say not to use on high milage vehicles."