Banfield is notorious for over-vaccinating.
Remember, most often the deadly reaction to lepto doesn't happen with the first vaccination. It's usually the second or even third shot, after the body has had a chance to build up antibodies, that causes the problems. Just because your puppy did okay with the first vaccination does not mean he will be okay with the booster.
Leptospirosis is a bacterial rather than a viral disease. Consequently, the canine lepto shot is not a modified live virus vaccine, but is a chemically inactivated bacterium containing more potential antigens (individual disease units) capable of causing reactions....Anaphylaxis does not occur after the first inoculation, but after the second or third when antibodies produced by the puppy’s immune system become hypersensitive. Anaphylactic Reaction to Leptospirosis Vaccine : NTCA Norwich Terrier Club of America