Each girl is different as to how "tight" or "loose" they are.. It has nothing to do with being skinny or not. Just how they were made.
Now as for your friend saying that 95% of girls bleed after being fingered.. That is wrong. The only time a girl bleeds is if her hymen was just broken (or if you prefer the term "popped her cherry") and the majority of girls have their hymens broken even before they have sex. Wearing tampons will break it, even doing something like horse riding can cause it to tear, not many girls actually do have it by the time they have sex for the first time, but if they do they might not even bleed either. Just a luck of the draw kind of thing. However if a girl bleeds (and you know for a fact that her hymen has been broken) it is probably because of a cut that has been made inside her, perhaps during rough sex, or even by someone who was fingering her that had longish fingernails.
Hope this cleared up some of the misconceptions that you may of had!