Apparently plenty of for sure hets don't have it. I don’t have a good explanation of why it should show up in some lines of hets and not in others.
Mine are all possible hets so I haven't personally proven anything. However it stands out as so different from nomal and I've seen it passed to half the offspring so I'm pretty confident in it. Some claim to see it in varying numbers of assumed normals. I'd like to see some pics to see if we are really talking about the same thing or not. I don't deny that there might be a few non-het for pied with the same belly but I don't think it would be very many and it might not be more than the number of hets you would expect from the wild at random.
Here is a pic of three 25% chance hets I'm growing up. The biggest one isn't positioned right to see the lines on the black edge lines on the last third of her white belly.
IMHO the possible het you posted is most likely a het.
