How does the memory of a 64bit and 32bit processor work
No, the author is wrong. 

I have used 32 bit processors that could address 64 GB of RAM. Memory is restricted by the number of address lines, multiplied by the number of bytes addressed by each individual value of address lines. 

Address space of one application was limited to 4GB, but you could have a dozen applications running at the same time, each using several GB. 

The author also seems to be quite ignorant of what processors and operating systems exist.