It isn't true, there were problems with the experimental work done. The research was released as a pre-print and hasn't yet been peer reviewed. It is being rubbished by lots of other scientists online.
Seems doubtful given the very low antibody levels, the covid test or the antibody test must be wrong for this to be true. If it's correct they we would be in full second wave territory then, and it's seasonal March-June for our part of the planet.