RFID refers to a family of technologies that operate over a variety of frequencies and given by the ISO standards. Specifically, 134kHz, 13.56MHz, ~915MHz, and 2.4GHz. The 13.56MHz standardized frequency for RFID is the same as that for NFC. The RFID ISO standards that specify the use of 13.56MHz are ISO 14443 and ISO 15693. NFC is specified in 2 ISO standards, but the more relevant to the discussion is ISO 18092 and it is derived from ISO 14443. So, there is some interoperability between ISO 14443 and ISO 18092, and therefore there is good reason to "conflate" NFC and RFID.
EDIT: I should cleanup and redact the Product Requirements Document I wrote 5 years ago for a transceiver board we built that could talk ISO 14443 and ISO 18092 (as well as ISO 15693) using a single transceiver ASIC and antenna tuned for 13.56MHz.
EDIT: I should cleanup and redact the Product Requirements Document I wrote 5 years ago for a transceiver board we built that could talk ISO 14443 and ISO 18092 (as well as ISO 15693) using a single transceiver ASIC and antenna tuned for 13.56MHz.