There seems to be some confusion on the Urban regs, so here it is right from the DNR...
"Urban waters have a year-round season, no length limits, and a special season (March 11 thru April 28, 2017) for juveniles 15 years of age and younger and certain disabled anglers. They also have a daily bag limit of three (3) trout, one (1) gamefish (largemouth bass, smallmouth bass, walleye, sauger, and northern pike), and ten (10) panfish (bluegill, crappie, pumpkinseed, yellow perch, and bullhead)."
All other regs not superseded by these special ones still apply, in particular:
This is from page 10 of the 2017 Wisc fishing regulations:
It is illegal to: to deposit fish carcasses or parts, including entrails or other waste, into Wisconsin waters or on the bank or shore of any water.
So the person who caught the pike was in violation for dumping it on the shore/bank. The size really has nothing to do with it.