Why are this monopole and dipole antenna so similar?
Whenever you see +2dBi gain, and the manufacturer has fairly measured gain to be 2dB above an isotropic radiator, then the antenna is more complex than a simple quarter-wave monopole. I would hesitate to guess exactly how the pig-tail top of the upper photo monopole attains its gain.
A simple half-wave dipole might have intrinsic gain near +2dBi. The one pictured in the bottom photo appears to be end-fed half-wavelength antenna with a low-Z to high-Z matching section buried in the connector shell. Arranged as shown, it would be vertically polarized...an end-fed dipole, rather than a centre-fed dipole.