The full passage of the second paragraph is:
During the Logistics Round of any Fair/Mixed weather
in 1941 only, German OOS Mechanized units anywhere
within range of an available Air unit may be given Air
Supply. Though Isolated German mech units are treated
as OOS on Turns 1-4 under rule 17.1.2, this rule has precedence
and Air Supply may never be given to Isolated
German Mechanized units. The Available Air unit may
supply up to six Mechanized units in range, and is not
flipped to its “Done” side after providing this supply.
More than one Air unit may provide such supply, but no
more than six German mechanized units in total may be
supplied in this manner per Logistics segment. The supplied
units do not all have to be in the same hex. Each
Mech unit supplied by Air has its OOS marker replaced
by an Air Supply marker. It is treated as fully supplied in
all respects, but has its MPs reduced by two. It remains
in Air Supply until the next Logistics Phase.
It seems clear that this is different from the air supply in the first paragraph. The restriction is to Axis mech on turns 1-4, because they have a special supply case that treats them as OOS, although they are isolated. This just says that isolated mech units that are being treated as OOS by the scenario rules cannot receive benefit from this type of air supply. On turns 1-4, there isn't any reason for them to use the first paragraph supply under 8.6.