Well, this is hard to explain but I will try my best. For some there would be no difference; many Asatruars believe exactly the same as many Odinists, however Odinists in general would have a more concrete or definite view of the gods, whereas some Asatruars may see them metaphorically as forces of nature, or not believe in them at all and see Asatru as an ancestral religion, but some others still believe in the gods in a literal sense.
Basically, the words mean the same thing, but an Odinist almost always believes in the gods in a literal way, whereas an Asatruar may not but also may literally believe in the gods. Sorry if that is confusing, but either term can mean the same thing, they just have different connotations...sometimes.
I personally describe myself as a heathen. I do not identify well with people who generally define themselves as Asatruars, while I do not believe exclusively in Odin so I find the term Odinist inadequate.
Personally I do not think the words mean the same. Then again, that's simply my view. I self-identify as an Odinsman, not an Odinist, because while I venerate all the Asa and Van, I feel an actual connection with the Allfather; and I feel a deep pang that remains in the connection between 'Odinist' and racism, even though I am well aware that Odinists are NOT racists by default [as much as anyone else is]; this is simply my own aversion.
I must though absolutely diagree that an asatruar would not believe in the Gods as individuals. I have never heard such a thing. Honestly I find such an assertion baffling.
None of the other Gods have ever really made themselves obvious to me, and that doesn't lower them in my eyes at all. I simply feel the Old Man in my life, and so it's to Him that I look, in general. Like as in a alarge family, some relatives you favor, see all teh time, and are involved with, and some you aren't, even though they're your family and go on with their lives knowing you are there as well. It would seem to me that an Odinist would also simply venerate Odin most; while Asatruar would seem a more general term that ~might~ include Odinists within. But again, I am speaking as I am, and not as a person who self-identifies as an Asatruar would.
Over the years, as a lone practitionaer, I've had to readjust what word I use as definitions were explained to me over time; but I haven't had the distinction you've mentioned made to me before; hence my comments.