Are hardlinks responsible for the bitcoin data directory appearing larger than expected?
The cumulative filesize of the bitcoind/bitcoin-qt directory has been a source of confusion since the introduction of v0.8 because it hardlinks multiple files within the directory. Briefly, two files point to the same data on the disk. So if you sum the size of the files, you don't get the total amount of data actually on the disk. In this manner, you can put 10GB of files on a 1GB USB, for example. 

Can I resume a blockchain download?

Yes, absolutely

Is blockchain.info is updated?

Currently, yes.

Is the size of the bitcoin data directory easy to understand

Somewhat, you need to understand hardlinks. Your OS might double count some files, leading to confusion.