I wonder if her friend was Korean. I used to live in Korea and the currency difference is about 10:1 with Japan. I spent a weekend in Japan and made the same mistake once. I saw a 10,000¥ wallet, mistakenly did the Korean mental math (1000₩≈$1) and thought it was $10 instead of $100. Luckily the cashier corrected me before I bought it.
I wonder if her friend was Korean. I used to live in Korea and the currency difference is about 10:1 with Japan. I spent a weekend in Japan and made the same mistake once. I saw a 10,000¥ wallet, mistakenly did the Korean mental math (1000₩≈$1) and thought it was $10 instead of $100. Luckily the cashier corrected me before I bought it.