How did they go from 16oz per prompt to 163 000 000 000 gallons of water?

1 prompt = 16 fl oz = 0.125 gallon^[1]^
1 year = 163 000 000 000 gallons^[1]^

163 000 000 000 (gallons) / 0.125 (gallons/prompt) = 1 304 000 000 000 prompts

Number of customer = 900 000 000^[2]^
1 304 000 000 000 (prompts) / 900 000 000 (customers) = 1449 prompt per customer (rounded up from 1448.888888..).

If all customers did 1 prompt/s it would take 24 minutes 9 second to reach 1 304 000 000 000 prompts (9 hours if they did it once per minute). That is by no means unfeasible but the number feels very arbitrary.

1: From the image
2: https://www.getpanto.ai/blog/openai-statistics