This is extraordinarily unlikely for several reasons. Like, beyond extraordinarily unlikely. (1) lemons are one of the least cold hardy citrus, any freezing will severely damage them and more than a few degrees below freezing kills them dead. They have no genes for cold resistance. Breeding lemons for cold hardiness is like breeding cacti to be aquatic plants–the genes just aren’t there, no amount of rearraigning or small chance mutation will fix that. (2) lemons, like many citrus, are highly true-to-seed. In this case, by true-to-seed, I mean literally clones. Many citrus, including virtually all edible citrus, produce a majority of seeds that are not the result of sexual reproduction, but of asexual cloning via apomixis. Even when cross-pollinated, most edible citrus will produce seeds that are mostly 100% genetic clones of the mother plant. Planting thousands of lemon seeds will get you thousands of the same lemon, and maybe a dozen actually sexually reproduced child plants. (3) there are several hobbyists breeding cold hardy citrus–ilya, walt, and kumin on the TropicalFruitForum being good examples of some who are currently active. None of them are simply relying on large populations of OP seed “adapting” to gradually colder and colder temperatures. All of them are relying on using hybrids of cold hardy but inedible wild citrus that were developed originally as rootstocks and are doing controlled backcrossing and very painstaking selection of the seedlings. The cold hardiness comes from the wild, inedible citrus (mostly poncirus, but also sour mandarins and some kumquat and ichang papeda, and some folks have talked about using Australian desert lime as well).
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