A little bit of background - I was living outside of the US for more than a decade and while I did have trips coming back to the US in SFO, over the last 12 years I had a single domestic flight.

Today I witnessed (and experienced) the following scene while going thru an ordinary (non-TSE Precheck) line: everyone in the line (which was half of the terminal long) at one point was stopped and then was ordered to walk in pairs about 30ft the same pace while a woman with K9 walking that dog (quite a large one) in front and past them while shouting 'walk the same pace, don't stop, don't interact!'.

What was this, how long has this practice been in place, and what purpose does it serve?

Apart from that and despite being scared that I am going to miss my flight (arrived 1.5h before the departure) surprisingly it took no more than 20 min to go thru the security. Another observation is that these body scanners are not in operation any more, everyone goes thru a plain old metal detector, and you don't need to remove your toiletries and shoes.

Is this some kind of temporary thing or policy change? Since when?