I’ve never met a bi person who insisted that they’re attraction to the genders were equal. Many had preferences (mostly into women, but defintely go with certain guys) and many had phases (more into men today, but was previously crushing hard on that girl). It’s one of the commonly talked about sources of bianxiety, that you can go through a period where you start thinking “am I really bi? Maybe I’m just straight / gay” and then you see someone and remember “no, I’m totally bi”. Bi erasure is such a thing it even effects bi folks! (source am bi, have lots of bi friends)
If you just want to know, without further investigation, that’s going to be very hard. People say a lot of things, and often aren’t clear themselves if it’s something they actually know, or just something they’ve heard. All that’s happened is that something interesting / helpful has popped into their mind and they’ve shared it.
If you are willing to discuss it, but don’t want to be rude by asking “do you actually know anthing about this?” you can just ask follow up questions, asking for more info / details. That way people who really know can answer, and people who don’t will probably just not answer or say that they just read it somewhere (often they’re not trying to deceive, just sharing something interesting they heard about).
But as others have said, just be sceptical of stuff you read, especially on the Internet. Lots of people have first had experience of something and still have unhelpful or strange takes on things. People massively over estimate how representative their experiences are, and if you get two experts in a room they’ll pretty soon be disagreeing about something they both know throughly.