No......it is not undigested food. There are a number of these all the same shape, texture, etc. if it was undigested food, my teeth would not have been able to cut them all quite so symetrically.it is extremely tough.....it does not fall apart.
Also, I know precisely what I have eaten over the last couple of days....and it does not include anything that could possibly look like that. I have only eaten freshly prepared veg, fruit some yoghurt and chicken.
Yes, it is a UK one pense coin for reference.