I assume his nationality is Prussian/German?
If so, then he could have been baptized (if the parents belonged to a religion that baptized infants) with at least one name of each of his witness/sponsors, as was the custom.
Some were kept... some were dropped.
It would then be up to the individual to choose his user name when reaching maturity/manhood.
Just because one name appears before the other does not mean a first, second or middle name.