On the phones I've seen, "BT tethering" would mean a GPRS/3G/4G modem interface using the DUN profile, not PAN. As a consequence, the connection can be used by only one computer at a time (hence "tethering").
The PAN profile would behave more like a WiFi access point mode of the phone, but over Bluetooth radio protocols instead of WiFi. In theory, multiple clients could use the same PAN access point at the same time (unless the phone specifically restricts that).
On any phone I've seen, the difference of BT PAN and BT DUN is apparently considered too technical for an average user, and so the terms are not readily visible. Since WiFi generally provides more bandwidth, BT PAN has become an uncommon choice. In areas with a lot of interference in the 2.4 GHz frequency band, BT PAN might trade bandwidth for increased reliability?
(If I recall correctly, instead of being restricted to 13 or so partially overlapping channels within the 2.4 GHz band like WiFi, a Bluetooth transmission will frequency-hop all over the 2.4 GHz band. So it might be more robust against interfering signals, but also more obnoxious for other users of the band if used for similar amounts of data as WiFi.)