what is the difference between utxo set bloat and blockchain bloat?

There is no difference.

Of course there is a difference. The UTXO set are all of the unspent outputs, against which new transactions are verified. The blockchain is the entire history of transactions up until now. If you want to run a full node, you have to store the entire blockchain. You don't however need to store the entire UTXO set with UTreeXO, only the outputs that you own.