Yeah my mom avoids eating pomegranate seeds and sometimes grape seeds because of similar proscriptions she heard from someone! I never read any respectable nutritionist say we should avoid eating fruit seeds for any reason, so for me it's probably a myth! We also have those guavas and we have our local prickly pears that have similar seeds that are impossible to break apart with your teeth, but we don't have any cultural proscriptions against eating the seeds.