Yes , it was a person other than Fleming. Fleming made the initial discovery, but others made it commercial.
Student or Learner
In 1928, bacteriologist Alexander Fleming made a chance discovery from an already discarded, contaminated Petri dish. The mold that had contaminated the experiment turned out to contain a powerful antibiotic, penicillin. However, although Fleming was credited with the discovery, it was over a decade before someone else turned penicillin into the miracle drug for the 20th century.
Does "someone" imply a person other than Fleming?
What does "over a decade before" mean? Did Fleming find penicillin and turn it into miracle drug 10 years later?
"someone else" doesn't "imply" it was someone other than Fleming. It states it outright.
"over a decade" means it was more than 10 years. Maybe 10 years and one month. Maybe 20 years. Probably more like 11 or 12 years.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.