He is the same guy from yesterday, not other (physical) guy. He is the same person as he was yesterday, he didn't (psychically) change. If John is the same (tall, heavy, etc) as Bill, we use ”la fel ca”. There is a distinction in Romanian, between equality, identity (identical with/to), equivalence, similarity, etc.
edit: contradicting myself... few sentences forward: „vreu aceiași pantaloni”=”I want the same pants”, that is ”like yesterday”, or ”like him/his”, which can also mean the same pair, or the same type/kind, but different pair. This is usually clarified from context, but here on Duo they keep it minimal to teach you the basics.
Thanks. So would one use "la fel ca" of things as well? Could the pants sentence also have said "vreu la fel pantaloni ca tale" or something?
Certainly. ”vreau pantaloni la fel ca el” (telling to the seller, and pointing to a third person present, with the right trousers). Sau ”vreau pantaloni la fel ca ai lui” (more correct from the grammar point of view). If you speak with the guy with the pants, you say ”vreau pantaloni la fel ca ai tăi” (not ”tale”, that is for female objects), (textual ”I want pants same kind as your pants (are)”), ori ”la fel ca tine” (as you (have)), the first one is better, the second one is a bit forced without an additional verb. Better would be ”vreau să am pantaloni la fel ca tine” (textual ”I want to have pants same kind as you have”), ”vreau să am (același fel de) pantaloni ca tine”, ”vreau să am pantaloni cum ai tu” etc. They are all correct forms.