The 20-year-old, who it has now emerged has learning difficulties, was said to be extremely sorry and remorseful.
The drama unfolded when crews were called to reports of smoke coming from an electricity supply box. The mains cable was linked to a house where electricity was being illegally diverted to power a cannabis factory with 300 plants.
Police say a man walked past the firefighters as they made the scene safe and pointed a handgun at two of the crew members.
A passing PCSO held on to him until police arrived at the scene in Gregory Avenue, Weoley Castle, Birmingham, at around 7pm yesterday on Wednesday.
West Midlands Fire Service said today: "Since this unfortunate incident, it's emerged that the young man who was arrested has learning difficulties.
"He's extremely sorry and remorseful for what happened, and our colleagues at West Midlands Police have released him with a caution.
"We've been in touch with his mum ourselves and are looking at how we can work with them to offer the young man some support and mentoring.
"We're pleased that these events will hopefully have a more positive outcome."