If someone snaps a photo of a subject in good light, because the photographer instinctively knows what will make a good photo, but the subject is just doing their normal everyday things? We still consider it accidental.
Remember that we’re not looking for photos that were accidentally taken, like the camera was yeeted through the air and this was the last photo it captured before it shattered. That’s not what Accidental means in our context.
It means a situation that was already happening, but the moment that a photographer caught just happened to resemble a painting from the 14th-16th centuries.
We draw the line at people purposely recreating Renaissance vibes with costumes, or people doing a pose that is heavily associated with certain Renaissance paintings, or elaborate lighting rigs used in professional photo studios made specifically to replicate the lighting in Rembrandt’s work (for example).
If the photographer was trying to make the mother and child recreate an exact Renaissance pose, they’re doing a terrible job at it, but the overall effect is Renaissance-like.