I don’t know how old you are, but saying “I’m bisexual” in 1976 was prior to the era of tightly defined sexual expressions in the area of homosexuality and bisexuality. In 76, to say it was to imply that you do it.
Like the Bible says, on the word of one witness, convict them.
Or was that two witnesses? On the Jagger incident, we have one. On bisexuality, we have Bowie’s statement, coupled with (1) no evidence he acted on it, and (2) his own admission that much of what he said was for publicity.
I remember in the movie "Saturday Night Fever", one of the scenes had the argument about whether Bowie was gay or bisexual. The one character said that "bisexual" meant that you like both. The other person replied, "Yeah he likes both....Men AND Boys."