If it was "dewinterized", there shouldn't be any antifreeze in the system. The water heater should have been in the "bypass" mode for winterization, and drained. When dewinterizing, the water heater remains in the bypass mode until the lines are completely flushed out. Antifreeze in the FW tank? Shouldn't be. Easy way to tell is to crack the FW tank drain valve and see what runs out.
'07 K3500 Silverado LT Crew Duramax (LBZ)
2016 Salem 27RKSS
1984 CHEV SCOTTSDALE K20 2GCGK24J0E1XXXXXX (Chevrolet Legends-Class of 2019)
"...exhaust fluid? We don't need no stinkin' exhaust fluid"