This is a question that you will ask yourself over and over again throughout the years: Is "this" adoption-related? And I think it's good, as adoptive parents, to keep asking that question. Even children adopted at birth can have extra challenges, at various developmental stages, that are related to their early life experiences, including in utero. Adoption itself can be a source of trauma, and some kids are more sensitive to this than others.
My rule of thumb has been that if my daughter's behavior seems out of the normal range for her age and stage, and doesn't seem to be responding in a typical way to "good" parenting practices, then it's been worth investigating if something adoption-related is going on. As a thread bystander, I have no way of judging this for your son, but as you have heard from others, toddlers frequently experience lengthy tantrums. Educate yourself about the range of "normal" and see what responses work best for him. Never be afraid to ask for help if you need it or if you're unsure!