They are talking about a situation when they are transporting a person to a mental facility for evaluation, which means they may not have been arrested. If they are arrested, cops do have the right to confiscate a firearm.
Cops should have the discretionary right to confiscate weapons from anyone they transport in a squad car. Period. I certainly would not want to transport a nutcase who was carrying a 44 mag and babbling about what a great president Obama has become.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." -- Benjamin Franklin