If you planted lemon seeds the resulting plants are lemons. They will not be true to variety but they will always be lemons- nothing "non-lemon" about them. Don't try and judge a plant by the appearance of the sprout- it's way too soon to tell. Of course it is always possible that a weed seed got in there, especially if they are outdoors. Birds deposit all sorts of seeds everywhere.

I would let it do it thing. It will branch when it is ready. When it is about 5 feet tall you will need to take a bud from the top and graft it to the bottom of the tree if you ever want fruit. wood maturity is messured by the tree as the number of leaves that bud is from the roots. At 5 feet you may have a leaf node count of 100.. the leaf node count will start at 100 even though the bud has been moved to the base of the tree.

Growing most types of fruit from seed is generally a bad idea. There is a high chance the fruit will not be as good as the parent variety. For those of you who are not aware of how this works, in nature fruit species can have a lot of genetic diversity from generation to generation. When a good producing tree is found, it then gets propagated from cuttings. People usually do not want to take the trouble of growing a fruit tree from seed when they do not even know whether the fruit will be good. Generally though, lemons produce truer to seed than oranges do. Not talking about citrus here, but for fruit trees in general, it is theoretically possible to breed fruit that produces truer to seed, but it takes many more generations of breeding. These are often traditional heirloom varieties that have been around a long time. Whereas the seed from a Navel orange will not really result in a Navel variety, some of these heirloom varieties can essentially be continually propagated from seed. The terms "heirloom", "true to seed", and fruit "variety" can all be very relative and ambiguous terms.

If you can post a photo, it would help a lot; also some information about your soil mix and your fertilization schedule and type. Most likely your Meyer is just suffering from the light change from where it was to where it is; Meyers are quite sensitive to significant light changes and will often drop many, most, or even all its leaves to replace them with new leaves better suited to the new light conditions. If you continue to treat the tree well, if should respond with new leaves and shoots in a short while.