they bought that off cray, but in 01995 a few months after they released java, they (a different division) released the dual-processor ultra 2 https://en.wikipedia.org/wiki/Sun_Ultra_series
but that wasn't sun's first smp machine; the sparcserver 630mp, among others, supported four cpus in 01991 https://en.wikipedia.org/wiki/SPARCstation#Server_systems
i had a dual-processor smp pentium pro under my desk by 01998, running windows nt 4.0 and occasionally java
really tho the bigger issue with java performance was that there was no supported native-code compiler until hotspot; though gcj was available, sun didn't support it, and i don't recall its performance as being that great. so by writing your code in java you were usually wasting 95% of your cpu on the bytecode interpreter, like python today. it wasn't something you'd do for things that required a lot of cpu
So Java's green threads was not a stop-gap for the 90s machine which only had one core. That's preposterous. Does Go need to disable its goroutines to support the Raspberry Pi Zero that has only one core? Obviously not! The reason Java didn't support multi-core scheduling is that multi-core processors still weren't a thing, and SMP was too high-end for them to bother (and by the time they did start caring about high-end systems, they've already moved to kernel threads).
Nothing prevents green threads from supporting multi-core (Java 21's Virtual Threads obviously do that, but Erlang's processes also had SMP support well before Go).
I think the terms "green threads" or "user-space threads" are really not that confusing. Definitely not confusing enough to warrant inventing a new term like "goroutines". THAT is confusing. I'm happy the Project Loom team resisted the urge to give the Virtual Threads a fun name like "Jorutines".