Yeah this work is far away from what a real PDF parser requires. It’s not uncommon for the lengths at the beginning of streams to be wrong or the data to be encoded in a format different from the one claimed. The offset table can also be wrong or missing.
Malformed file is a whole another can of worms a good parser should know how to deal with but here it doesn't even format compliant.
I think they wanted to demonstrate that their work can slice a stream by offset table, in a declarative fashion. It is a useful property. I think they would've better picked OTF/TTF for demonstration of this particular feature.
