Right. Every sign of interest a woman gives you can be used for attention, rather than actual interest.
I've tried to stress looking for multiple signs in the article: the sign, plus other behaviors, etc. If you want higher odds to tell if she's interested, look for multiple signs. If you want to know for sure if she's interested, ask for compliance (it's the only way to know for sure).
As far as bumping/clumsiness... the "girl running into guy in the hall" was the only good example I could find for this. Couldn't find pictures or GIFs of a girl knocking into a guy's table or dropping her pen right next to a guy. They might be cliché, but girls do them... they're cliché for a reason. Maybe because they're cliché, a lot of guys seem to think when it happens "Oh, that's a cliché. She wouldn't actually do that for real if she was interested." Which is... not the right takeaway. Women copy each other and do things they see other women do (they're also just clumsy in general, and clumsier around guys they like).
I have seen women doing those things to other men and I could clearly tell that they weren't really interested in them.
Yeah, maybe! Any sign of interest that gets a reaction out of someone else can be used for ulterior purposes. There are no 100% signs.
However, on the other hand, careful about being too certain in your readings. I've spent a lot of time in the field and am pretty good at reading things most times... however there have still been plenty of times I've seen a girl with a guy, said to myself, "She's just playing him. She's not interested in him at all," only to see the two of them leave the place later or start making out. Likewise, I've had my fair share of girls around me about whom I thought "Eh, she's not really interested", but followed good process and asked her to come along with me anyway, only for her to say yes. I've bedded a not-insignificant number of women like that too. One of my best girlfriends and longest relationships was with a girl about whom I was certain, right up to the moment we fell into bed, that she was not actually interested in me romantically.
Predictions are useful. But you always need to be wary of about assuming you've got it totally figured out. Sometimes the girls who seem like they're for real aren't, and the ones who seem like they're playing games are in fact legit.