Unfortunately the answer is to look closer (also to use a high resolution reference image) - a sliced kiwi actually does have cast shadows - the seeds sit inside these little furrows in the kiwi's flesh, so even though it's very subtle, there will be slight shadows cast into those sections from the higher part of the surface to the lower. The thing about figuring out the shadows is to actually consider the forms that are present. Thinking about what that surface would feel like if you ran your finger over it can help a great deal in identifying where the raised/lowered forms would actually be, so you can better identify them in the reference image. Alongside those grooves, there's also the flesh itself which isn't entirely smooth, and instead is made up of a subtle pulp (resulting in an uneven surface made up of many little forms).

It's definitely a challenging thing to consider, and people are generally not used to thinking about surfaces in this way. Just always remember - unless a surface is perfectly smooth, there will be a variety of forms present upon it.