This is the common response being heard a little extra these days as Metro buses appear to be taking over the Sound Transit routes. Why the confusion? Well, METROs Fares page does say "Metro Paper transfers are only valid on Metro buses". So this leads to the confusion when a Metro bus is substituted in, and when one ST route overlaps a Metro route, and not everyone reads signs, just notices the equipment, it makes it a bit harder for the operator to explain.
As of late ST Buses that serve the east routes have been caving in left and right , leaving no choice but to run the service with Metro equipment, From Metro Hybrids to the D60s and even a few Gillig 3200's. 13 brand new shiny ST Hybrids are about to take to the streets shortly, and a handful more are on order! In the meantime, you may get a variety of equipment so Sound Transit and Metro can still get you there.
As a reminder, Sound Transit Routes do NOT accept paper transfers. If you have an ORCA card, you can transfer between Metro and ST as you always have.
METRO transfers are only good on METRO routes, nothing else, .......well, maybe a bookmark too.