I supposedly have a Meiwa Kumquat tree, but most of the literature I have read says that the Meiwa do NOT have thorns. The fruits have been fairly spherical (like they should be) but the tree does indeed have a few thorns. Could it be another variety?
If the leaves, the flowers, and fruit look right (and taste right in the case of the fruit), I wouldn't worry too much and just chalk it up to genetic differences among the same plant species and enjoy the plant. Compare the fruit to pictures of what it should be and look at the flowers and leaves. If it was grown from seed, there is no guarantees that it is not a hybrid, and if it is a graft, it may have some different characteristics due to the environment it has been growing in or due to variations in the plant it came from. Without pictures though, most of the people who know what a mature plant of this type looks like will not respond because they can't tell you without seeing it. So if you want a more definite response, find a camera and snap a few pictures of the whole plant and some individual branches. If these show the fruit and/or flowers that is even better!
