US case law does not apply worldwide and might not even apply in more than one state unless it was in a Federal Court.
there is block exemption for cars and vans initially in the EU and now in UK as well as we adopted the same law post Brexit
when the block exemption was created, motorcycles were not included
block exemption means that as long as you can demonstrate the correct parts and service schedule were used, the manufacturer has to honour the warranty, regardless if it is a home service or using an independent. This was a law advocated for by vehicle leasing companies who undertake their own servicing such as Lex. They had no interest in bikes when they lobbied the EU Commission
this has been discussed many times in this very forum