Which part do you find hard to believe? That people with aphantasia can have a hard time with the method of loci, or that aphantasia is more common for software engineers than in the general population?
Well, there's a paper from 2020 that suggests that people with aphantasia are more likely to be working in a scientific or mathematical occupation: https://doi.org/10.1016/j.cortex.2020.04.003
Anecdotally, one can also search for engineer on the aphantasia subreddit to find many threads with engineers chiming in.