I went to https://www.ruby-lang.org/en/about/ and I didn't find any references to trademarks. There is a JRuby, an IronRuby, why not a Rooby?
IronRuby and JRuby are both implementations of Ruby; aside from any trademark issues that maybexist (I kind of doubt there are any) the usse of Ruby in the name is communicative of accurate information. Using something that's natural pronunciation is as a homophobe of Ruby for something that is not a Ruby implementation is probably misleading and and undesirable for it's effect on being able to clearly talk about the project.
I believe the two could be sufficiently differentiated in execution to satisfy the USTPO. It's a rather subjective system.