The 68-year-old professional fugitive finder opened up about the alleged altercation during an interview with The Sun.
According to Dog, Gabby was "very verbal" with Brian, who he claims "usually" put his hands on the late 22-year-old vlogger in an alleged attempt to calm her down.
"I know that she was very verbal because as they were arguing one time, the vacationers around them heard her yelling," the reality star told the outlet.
"I know that he calmed her down usually by grabbing her mouth like this because when you grab someone’s mouth like that you know she was verbal," Dog added.
Despite throwing out the claim, Dog failed to clarify which vacationers or alleged incident he's talking about.
The engaged couple was reportedly seen fighting at a Wyoming restaurant on August 27. According to witnesses, Brian was acting "aggressive" towards a number of females inside the establishment and Gabby was "crying."
That was the last time anyone reportedly saw Gabby alive.
That wasn't their only fight during their months-long trip.
On August 12, Gabby and Brian were stopped by Utah police after a concerned citizen called 911 and claimed to see him "slapping" her.
Body-cam footage shows a sobbing Gabby telling officers she hit Brian and she suffered from OCD and anxiety. Moab police chalked the whole thing up to a mental-health crisis and not a domestic incident.
A second body-cam video was later released and told a slightly different story.
Gabby's body was found in Wyoming on September 19 near a campground the couple reportedly visited. The coroner ruled her death a homicide but has not disclosed the autopsy report.
Brian returned to his family's North Port, Florida home from their cross-country trip in their van alone on September 1. Gabby was reported missing on September 11.
On September 13, Brian allegedly told his parents he was going on a solo hike in the Carlton Reserve. They waited four days before announcing their son was missing.