I think that it was mistranslated. I have seen Yonisomanasikara translated in this way, and in the translation I was reading, one section used "careful attention" and then when this didn't fit later in the reading, the translator changed it to "reflection." So it seems that even the translator was confused. We prefer to go by the Pra Prayutto translation. He is fluent in English, Thai, Pali, and he is the foremost Buddhist scholar of Thailand. He translates Yonisomanasikara as "Wise Reflection." The translation "carreful attention" doesn't fit for some of the particular examples where Yonisomanasikara is indicated in the scriptures. Careful attention implies more mindfulness rather than contemplation.
These mistranslations are confusing a lot of people. Usually these mistranslations seem to come from people who actually have not been taught about Wise Reflection meditations and have been taught a lot about mindfulness, but don't understand the bigger picture of mindfulness.