Indeed. The header field Cwt/v (created with version, at offset 0x28) has the value $00. I checked other files, and they have $27 instead. Either the tracker used to create/modify this song did not write the Impulse Tracker version or it has been manipulated with a hex editor.

I don't know if this somehow affects playback in OpenMPT.

Probably not,though the eight bit version of that song displays as being created with ModPlug, and the 16 bit version displays as that. It may or may not affect MPT hacks.

8bit version: ftp://ftp.modland.com/pub/modules/Impulsetracker/Ceekayed/ancardia%20(8%20bit).it

Yes, there are some files out there with weird "saved with" values. In this case it can be ruled out that it was saved with ModPlug as its file header does not show some of the quirks that older MPT versions would emit. It could be saved with a very early / experimental version of Chibi or Schism that I don't know about, or it could just be hand-edited. There's nothing we can really do here.

Well, we at least should not claim "Impulse Tracker 0.00." We could just be honest and say "unknown" or "Unknown Tracker (Version 0.00)" or something along those lines.

r10733 adds a special case for v0.00.