Honestly, historians are just cagey about anything that can be argued about. Typically they wan't to use language that is either verifiable or culturally specific (e.g. pederasty). One lecturer I know also emphasised that direct equivalency can be frankly problematic (e.g. lots of examples of Roman "homosexuality" is older men and younger boys). At the end of the day we can't speak to identity in most cases, and that identity will be culturally situated. We can talk about actions. Can't say if Julius Caesar was bisexual, can say he probably had sex with both men and women. Does sound like tiptoeing around to people used to saying "gay" not "men who have sex with men".