He claims you cant have spaces and question marks in Unix. I found this confusing because I do it all the time. Its true you need escape characters that you can enter manually with a \ or you can do it automatically by wrapping the filename in "double quotes"
He claims that in unix renaming files is scary because links to a file would not follow a renaming of that file. He specifically calls out both hard links (aka physical links) and softlinks (aka symbolic links). However It is the very point of physical links that they point to the inod not to another path. I have just verified this and it is very much true that physical links follow renames. Moreover, when building the kind of Rube Goldberg machine that file systems are used for, being able to have links that don't follow a rename, and ones that do is very useful.