Dam external app module bootstraps assetImage dialog into stk config.modules.standard-templating-kit.dialogs.generic.pages.assetImage.xml, but module has no dependency on stk. So dialog is bootstrapped also when stk is not in webapp.
Dam external app should have optional dependency on stk and dialog should be bootstrapped only when stk is in webapp. Or Dam external app should not bootstrapped the dialog at all so no stk dependency is needed.