Do you think that the stains next to the filling are cavities?

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The stain does not seem to be a cavity by seeing the picture (attachment removed to protect patient identity). Sensitivity and pain while flossing seems to occur due to the deep filling and food impaction between those teeth. Also, the two metal filling are touching each other, which should have been avoided as they create a small positive negative electrode effect due to constant movement while chewing and create a small charge, which will cause high sensitivity at times. At least, one filling should be replaced with a composite material to prevent sensitivity. While doing it the dentist will reshape the contact point, so that it does not pain while flossing and the area cleans properly without causing food impaction.