Does anyone undestand this sentence?

  "Most of these close-in planets were found to be roughly between the size of 
  Earth and Neptune, which is about 4 times the size of Earth."

Wikipedia says Neptune's volume = 57.74 Earths and Mass = 17.147 Earths. https://www.wikiwand.com/en/Neptune

Neptune radius: 24,622 km

Earth radius: 6,371 km

That's your 4 times the size measure.

Correct. Transit methods measure size not mass.

neptune is 3.86 earth diameters, based on the wikipedia values.

They're probably referring to the diameter.