What ☆SleepyDreepy☆ says is correct. I'm not sure whether PS! has different mechanics from Pokemon Games, or it was a glitch or bug. According to Bulbapedia, there has been no changes in damage modifier in the generations. See the changes:
Gen V
> Stealth Rock can now be reflected by Magic Coat.
Gen VI onwards
Defog now clears Stealth Rock from both sides.
Stealth Rock is unaffected by strong winds. In an Inverse Battle, Stealth Rock uses the inverted weakness and resistance to Rock to calculate damage.
Stealth Rock can be used as part of a Contest Spectacular combination, causing Circle Throw, Dragon Tail, Roar, and Whirlwind to give extra three appeal points if used in the next turn.
Any Pokémon that appear after calling for help during SOS Battles are subject to Stealth Rock.
If powered up by a Rockium Z into Z-Stealth Rock, it will raise the user's Defense stat by one stage.
Using G-Max Stonesurge will set up Stealth Rock on the target's side of the field.
Source
I would want to test it myself, but right now no one is free and I can't challenge myself.
