My lemon tree was cut down very low by the person cutting my yard. The tree was about two years old. It was cut with a weed eater.
The smaller the tree was the more likely it is to grow back. Trees put on new growth by activating dormant buds along the length of the trunk. The smaller the branch or trunk the more dense those buds are. Be sure to keep grass and weeds growing around the stump/stub cut back and let light get to the bark.
Unfortunately no one can tell you for sure if your lemon will grow back until time has passed. Citrus trees are capable of growing back, but it's not guaranteed like it is with a willow or poplar tree for instance.