Is a 401k plan considered a "Traditional IRA" for purposes of inclusion on Line 6 of Form 8606?

A previous answer from shellsbush180 indicated that the answer to this exact question was "no".  But this implies that a 401(k) is excluded from calculating a RMD.  I that were true, why would anyone convert a (no basis) 401k to an traditional IRA, if the 401(k) was able to grow indefinitely, with no required distributions?