Note that this was probably 100% equity (or close to it) so the Bitstrips people may have gotten far, far less than $100M if Snapchat's valuation is still as delusional as it used to be.
On the flip side, it's possible that they got the "$100M" number because they know that they options aren't worth as much as they say on paper, and thus they asked for a higher paper value in order to compensate.
and they got common stock, ie buried under an avalanche of preference
That's not actually entirely true. Snapchat is known for having only preferences for seed/A round investors.