h1b case status : My document was mailed

my wife (working in a startup ) got her h1b picked this year. The case status says My document was mailed . We mailed your document for your form I-129 , petition for non immigrant worker , receipt number WACxxxxxxxxx . what does it mean ? She got her receipt notice few days back . But generally when we get our receipt notice status wud be different . Anyone got such status recently and what does this mean ?