Short answer: public space on the south side of the Barclays Center becomes private space, just as it does on the north side of the arena. And it's dangerous
First, a pedestrian walking east of Flatbush Avenue on the north side of Dean Street (see annotated photo below) had to walk in an improvised pedestrian lane caused by the construction fence outside the B2 modular tower, aka 461 Dean Street.
But, as shown in the photo, a truck was wedged in near the area where the road was cut off, and an SUV used as a limo narrowed--if not blocked completely- the pedestrian passage around the B2 construction site and the bicycle lane.
So the pedestrian would be forced into the street. According to the report, the limo driver as well as Flyte Time International limo employee talking with him (same company?) acknowledged that they use that area until police shoo them away. According to the report, the police were sent over, so we don't know how long that situation persisted.
A longer look at Dean Street shows many more vehicles occupying public space. According to the report:
The turning lane included a bus, an emergency response vehicle and multiple limos. It is hard to know if this is the bus the NBA apparently requires, but may not allow to be dependent on the loading dock elevator. The below grade portion of the arena was reduced in 2009 and has never had enough capacity to support arena operations. Likewise, to save money the developer delayed building the below grade parking adjacent to the arena which was supposed to be opened around the time the arena opened. As a result, arena operations that was meant to be below grade continues to spill out into the neighborhood and its public spaces