These particular ones do not appear cantilevered.Those bollards can be extremely effective:
They look like temporary slide-in/slide-downs.
Rather than having deep poured concrete encased steel.
The ground grooves shown could not have been more than 2" thick, if true meaning a solid steel rod could be placed in a receiver and temporary waffle-construction removeable bollards bolted over that.
I'm just speculating from what was shown, and reports have come out that the driver negotiated the barriers.
Fail at any rate.