Looks like the server does it. According to man ftp: 
            For mdelete and mget,  each  remote  file  name  is
expanded separately on the remote machine and the lists are not
merged.

[download]
Of course, if you really want to know how it's done (and you have root access), a packet sniffer is your friend.

In reply to Re^2: Net::FTP wildcard delete? by dsheroh
in thread Net::FTP wildcard delete? by cormanaz

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