A. Color is not the correct way to determine PETG vs ABS. There are color variances, they can appear the same or different. Even when using the exact same filament as Prusa.
B. Shininess can change dramatically based on the temperature used to print the part, so it is also not the correct way to determine PETG vs ABS.
C. Prusa explicitly stated on the forums that the shroud is ABS.
D. Not all ABS is the same, some withstand more heat than others. Furthermore, different print settings can affect how much sag there is.
Conclusion: the only way your shroud was PETG was if you printed it yourself.