Do B/T cells form from lymphoid tissue or bone marrow?
This is a good question and I can see where some confusion can arise. Lymphocytes are a class of cells that include both B and T cells among others. They both have the same precursor cell that being a small lymphocyte [1,2]. The small lymphocyte will grow into a large lymphocyte then differentiate into a pro-B-cell or a pro-T-cell [3]. After differentiation the pro-B-cells are "trained" in the bone marrow and the pro-T-cells are "trained" in the thymus [4,5]. The processes of training for both B and T cells are active areas of research and are quite interesting if a bit confusing. 

from [6] 
"Lymphoid tissue has several different structural organizations related to its particular function in the immune response. The most highly organized lymphoid tissues are in the thymus and lymph nodes, which are well-defined encapsulated organs with easily identifiable architectures. In the spleen (a soft, purplish organ lying high in the abdomen), the lymphoid tissue is a cylinder of loosely organized cells surrounding small arteries. In the bone marrow this tissue is mixed with the blood-forming cells, and no organization is apparent."

It is true that red blood cells are produced in the bone marrow and are somewhat related to lymphocytes. They are cousins to each other in some way [7]. 

I hope this helped show the differences in the maturation of T and B cells and cleared up some confusion for you. If you would like to know more I would recommend picking up an immunology book. I used this one [8] and quite liked it when I was taking immunology. 

[1] https://en.wikipedia.org/wiki/Lymphocyte

[2] https://medical-dictionary.thefreedictionary.com/small+lymphocyte

[3] https://www.researchgate.net/figure/Life-and-death-decisions-during-B-and-T-cell-developmenta-This-panel-is-a_fig2_8014354

[4] https://www2.nau.edu/~fpm/immunology/Exams/Tcelldevelopment-401.html

[5] https://www.researchgate.net/publication/6196234_B-cell_anergy_From_transgenic_models_to_naturally_occurring_anergic_B_cells

[6] https://www.britannica.com/science/lymphoid-tissue

[7] https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0022042/?figure=1

[8]https://www.amazon.com/Basic-Immunology-Functions-Disorders-Immune/dp/032339082X/ref=sr_1_7?ie=UTF8&amp;qid=1524514359&amp;sr=8-7&amp;keywords=immunology