Most certainly a code violation. UPC 610.1 Size Of Potable Water Piping. "...size base on total demand, designed to ensure maximum velocities are not exceeded."
The corrosive resistance of copper pipe is due to an oxide film that naturally forms on the interior walls when in contact with flowing water. If the velocity is too great, impingement, or erosion corrosion occurs, stripping the protective oxide coating and damaging the pipe. Impingement damage occurs when water velocity exceeds eight feet per second in cold water.
There are numerous other code section violations, UPC Table 610.4, building supply, not less than 3/4 of an inch nominal size. "Installation Standards" violations. Too many enforcable violations to list.