This is just a guess, unless you can attach the ATC recording to prove this is what actually happened.
A guess? Perhaps - but not mine:
".....on an ILS approach to runway 16R cleared to land on runway 16R, when tower offered a visual swing over to runway 16C, the crew opted to accept runway 16C but aligned with taxiway T in between runways 16R and 16C and continued for a safe landing on taxiway T at 08:31L (16:31Z), no other traffic was on taxiway T at that time."
Incident: Alaska B739 at Seattle on Dec 19th 2015, landed on taxiway