Arguably, a majority and certainly a large minority of self identifying straight people picked that identification due to a fad. That one time you kissed another girl and boy was it hot? That one time another guy wanked you off? That one fellow in middle school you had a very clear intuition that you'd find him smoking hot if only you were into boys, but you aren't, right, so those thoughts must be something else? They don't count, right?
They don't count because you chose not to count them. You could just add easily count them as evidence that you're bi.
I don't think that classes as bi. "Straight" doesn't mean absolutely zero attraction to the same sex, just something well below the level you would ever act on it.
"Straight" doesn't mean anything other than what the community of English speakers wants it to mean. It's a funny habit words have.
However, if forced to provide their dictionary definition, must people would probably come up with something like "exclusively attracted to the opposite sex/gender".
Anything that is not 0% or 100% is part of a continuum, and if you want "straight" to mean something less strict than 0, any line you draw becomes arbitrary and subjective, and anyone else gets to draw their own line without either being "right" or "wrong". People tend to call themselves "straight" when they feel that whatever level of attraction they experience for the same sex is insignificant enough for who they *are* that bragging about it is just not worth the hassle, and be it only the hassle of having to do more explaining. But that's still a very subjective - and context dependent - line. If the hassle of identifying as anything other than straight is big, people you and I would probably call mostly homosexual will call themselves straight. If the hassle becomes smaller, people with a set off behaviors and preferences you would deem insufficient to call yourself "bi" may end up doing so - but they are not wrong to do so, or following a "fad", as someone has said upthread.