ἄνδρα μοι ἔννεπε, μοῦσα, πολύτροπον, ὃς μάλα πολλὰ/ πλάγχθη, ἐπεὶ Τροίης ἱερὸν πτολίεθρον ἔπερσεν./...
μῆνιν ἄειδε θεὰ Πηληϊάδεω Ἀχιλῆος/ οὐλομένην, ἣ μυρί᾽ Ἀχαιοῖς ἄλγε᾽ ἔθηκε,/...
Yes, Siam starts as Japanese-controlled, and Japan gets the income from it. As to why there are no units in it, not all territories start with units in them.
Just to add to this perfectly correct comment, when I first got this game I found an official FAQ on-line which stated in no uncertain terms that Siam starting without any units in it, although considered Japanese controlled, was not a mistake and in fact corresponded to the real historical situation the designer was trying to emulate. I don't know if that FAQ still exists but it was on the Wizard of the Coast website.