Long shadow illustration and consistency? [migrated]

I'm working on an app that is currently just flat icons and flat layout i.e. no use of drop or inner shadows anywhere. Unfortunately I can't share the layout of my app because of proprietary reasons. The app has a reddit app style sectioned layout]1, without the social buttons on every card because it's not a social app. I designed a material design style error illustration for any of the sections that don't load. Something like this.

I got some feedback that this would require us to use this type of material design style everywhere on the app- icons etc. I'm not sure if that makes sense?! Is using the longshadow illustration for errors require me to use material design everywhere else. From a methodology/theory standpoint- is it necessary? As mentioned everything else on the app like icons are flat. The reddit example is close in that style I'm talking about.