That's because your cab is also IFTN, which happens to give the same ID as the ECI modem. Here's some saved output from my TP-Link TD-W8970, on ADSL2, my exchange vendor ID is TSTC:
~ # /firmware/dsl_cpe_pipe.sh g997listrg 0
nReturn=0 nDirection=0 G994VendorID=IFTNTD SystemVendorID=IFTN VersionNumber=0123456789012345 SerialNumber=01234567890123456789012345678901 SelfTestResult=0 XTSECapabilities=(05,00,04,00,4C,01,04,00)
~ # /firmware/dsl_cpe_pipe.sh g997listrg 1
nReturn=0 nDirection=1 G994VendorID=TSTC SystemVendorID=0000 VersionNumber= SerialNumber=00000000000000000000000000000000 SelfTestResult=0 XTSECapabilities=(00,00,04,00,0C,00,00,00)