Where do you see the "huh?"
If you look at the score/listen to the Adagio of the Bruckner 7,
Leinsdorf is correct. The opening theme is basically repeated without
any real harmonic variation, let alone any development, when it
reoccurs. Bruckner adds some figurations in the violins - as pointed
out by Leinsdorf - but little else changes.
I disagree with Leinsdorf in his calling the opening theme of the
Adagio a "subject," because the word "subject" when used in a
classical music context implies something much more specific than a
theme. It implies a theme that can be subjected to variation and
development, and short, motivic subjects - ie: the kind often employed
by Beethoven - lend themselves to variation and development much more
readily than does the kind of "endless melody" that Bruckner provides
in the Adagio of the 7th.
So, IMHO, Leinsdorf is criticizing Bruckner for not doing something
that Bruckner never had any intention of doing in the first place. The
fact that the opening theme of the 7th's Adagio returns pretty much in
tact harmonically and melodically shows that Bruckner isn't interested
in writing a theme from which he can produce variations, but rather in
providing an anchor to the movement that serves the same function as
does a Rondo theme when it makes its expected re-appearances within
that musical form.
Leinsdorf also fails to recognize that Bruckner's musical citation of
the "non confundar in aeternum" theme ("let me never be confounded")
from his "Te Deum" in the principal theme of the Adagio rather
precludes him writing variations on that theme, as one of the
principal beliefs of the religious is that god does not change, that
his promises are kept, and that hope of a promise fulfilled is what
gives the believer the clarity of vision that keeps them from being
"confounded," no matter what else arises...which, in the case of the
Adagio under discussion, are the subsequent musical themes of
increasing beauty that are offered as an enticement away from the main
theme, but that are discarded by the true believer (Bruckner), who
takes the promise of "non confundar" seriously, and who returns again
and again to his opening "non-confounded theme" with no harmonic
variation, but with a more-intense/vibrant orchestration that serves
to build a stronger and stronger edifice against those themes trying
to pull the believer away from the main, non-confundar theme..
At least, that's what I think today.