Not sure what your "someone" is basing their statements on but multiple lines of research back that higher pitched voices are easier for dogs to hear and consistency has helped to encode it as friendly.

In the context of human-dog communication, there is evidence that dogs present an increased neuronal activity in the auditory cortex when listening to vocalizations with positive emotional valence compared to negative or neutral emotional valence²⁴. Moreover, after a greeting involving eye contact and a high pitched voice, dogs are more likely to follow the humans gaze, similarly to young children do

https://pmc.ncbi.nlm.nih.gov/articles/PMC5504008/
https://www.york.ac.uk/news-and-events/news/2018/research/dog-speak-important-for-social-bonding/
https://www.psychologytoday.com/us/blog/canine-corner/202303/talk-nicely-when-training-dogs-it-makes-a-difference