Yes, it is counterintuitive. And also not what is actually claimed in the paper.
In the paper three designs are compared:
(1) One with only an antenna on chip. That is, an antenna on the actual chip, with a size of 1x0.5 mm. Draws 3.3 mW, "range" 1m.
("Range" is a very strange measure in RF design...)
(2) The same chip but without the on-chip antenna. Instead the power is coupled to an additional PA-amplifier, and an external small folded dipole antenna: Size about 16x10 mm. Draws 38 mW, "Range" 75 m.
(3) The same chip withou the PA, with the on-chip antenna coupling to an external patch antenna of size 17x17 mm. Draws 3.3 mW, "Range" 24 m.
In summary: Nice engineering work, but no conclusions can be drawn, as it is very much a case of apples and oranges. (No constant TX power, No constant size, Not very much constant between the designs at all.)
And a classic mobile phone does not use an on-chip antenna at all. So this design will not give any benefit to your iPhone or Blackberry etc.