Are you kidding me? $5 billion usd,? What did they do with all the money then,? I understand this might be a mistake maybe you meant to say $5 million dollar which is still a lot of money to begin with, but ever since I got into crypto, I've never heard of any ICO or IEO raising as much as $5 billion dollars, but anyways, anything is possible.
And back to the question whether polkadot is a scam, it is not a scam, all crypto assets are volatile, they up and down, and sometimes, if their price go down significantly, they loose their position or coin market cap, this does not necessarily mean it's a scam.