That changes everything. They shoulda just said 50.5 billion and then I wouldn't have been stupid.
It's an artifact of there being two different numbering systems, the 'short scale' and the 'long scale'. In the short scale system, each named unit is 1,000 times the next lower unit -- so a million is 1,000,000, a billion is 1,000,000,000, a trillion is 1,000,000,000,000, etc. -- while in the long scale system, each named unit is 1,000,000 times the next lower unit -- so a million is still 1,000,000, but a billion is 1,000,000,000,000 and a trillion is 1,000,000,000,000,000,000. (in the long scale system, a thousand million is a 'milliard', which was later extended by construction of a 'billiard' being a thousand billion and a 'trilliard' being a thousand trillion.
Reporting a number as 50,500 million avoids confusion over the base unit in countries that use the long scale system, although that usage introduces an additional complication -- in Europe, Russia, South America, and several other countries, the decimal separator is a comma, which makes "50,500" read as 'fifty and one half', not 'fifty thousand five hundred'.