This happens when you get a minimal level of infection in your body due to corona virus for which your body fights back by producing the antibodies which your report says . May b u got a minimal infection which left you assymptomatic and u dint even know when n where from u get that infection which lead to the production of the antibodies . Don't wry it's normal. If ur symptoms develop at any time , plz get an RT PCR test done for corona virus.

Do a RTPCR