I don't know his reasons, but I also try to avoid third party because 1) Often you can do the same with the standard library with very little extra code. 2) Using lots of third party makes your code less maintainable. A lot of little libraries are not well maintained. 3) You are at the mercy of when the third party library updates to fit say latest language version or standard libraries. 4) Third party libraries can pull in a lot of unwanted complexity. You might only use a tiny tiny part of it. 5) By relying on third party you force other developers to know that library in addition to the standard library.

There is a certain amount of trigger happiness around when it comes to third party libraries. People tend to use third party libs WAY TOO much. Often they don't even check what is in the standard library.

I've thrown out over 50% of the third party libraries used in iOS projects I've taken over while simplifying and reducing the amount of code. The reason why using the third party libs grew the code was that third party libraries are usually quite generic, which requires more code to adapt to them. If your needs are quite simple, custom tailored code can take less space than utilising a third party library.