Unlikely that it was something decent like Truecrypt volumes and more likely nested encrypted zips/RARs.

Since the vast majority of these are encrypted with a simple text passcode, dictionary attacks are pretty routine against them.

http://home.schmorp.de/marc/fcrackzip.html

http://rarcrack.sourceforge.net

(as two examples)

Exactly. No one nests truecrypt but people do nest zips because the filenames are still visible with the older zip "encryption" format.

Are Truecrypt volumes with similarly bad passwords any harder to crack?

No. Good passwords are paramount.

Yes, most likely the password used a common word or something else similar susceptible to being brute-forced.