Help in understanding a sentence about TCR-MHC interaction and immune synapse formation
Does it mean that after a TCR binds to a peptide-MHC complex, other TCRs present on the cell gather around that TCR?

Yes. Other TCRs bind other MHC/antigen complexes and they all cluster together, forming an immunological synapse.

Does it mean that one TCR can bind more than one peptide-MHC complex (which, as far as I understand, isn't true)?

No. TCR:MHC bind 1:1.
Your final paraphrase is correct.