It would seem the scion is at the base of your plant, as shown in the second picture. Therefore, the branch you're concerned about is not a sucker because it doesn't arise from below the scion, or graft, or from below soil level. It might be a watersprout, although it doesn't look overly vigorous, and you will know whether its growing much faster than the rest of the tree. If it is growing much faster than the rest of the plant, then you might want to remove it, or you may want to remove it because you're restricting the plant's size. So called watersprouts usually arise from adventitious buds on the stem or on thick branches, and are often caused by excessive pruning - but that's something you're probably having to do because your plant's in a pot.
From its appearance in the photograph, it just seems to be a new branch - but you may not want it that low down. With regard to pruning, you should really cut off the nubs or stubs where you've pruned back - you need to leave a small collar at the base of a branch you remove, but its best not to leave remains that stick out for an inch or so, you're more likely to get dieback.