Is he getting Safari to reopen with windows that were there when he closed it? If so, from the menubar:
Safari > Preferences
... and then in General change the top selection box, 'Safari opens with', to 'A New Window'
If not, it might be a malicious plugin/extension that he has mistakenly installed? Try disabling all plugins in the Security tab of the same preferences menu, disabling and removing all extensions in the Security tab of the same preferences menu and remove all website data.
Is he getting Safari to reopen with windows that were there when he closed it? If so, from the menubar:
Safari > Preferences
... and then in General change the top selection box, 'Safari opens with', to 'A New Window'
If not, it might be a malicious plugin/extension that he has mistakenly installed? Try disabling all plugins in the Security tab of the same preferences menu, disabling and removing all extensions in the Security tab of the same preferences menu and remove all website data.