No, this is not a proof because not using Mizar ;-) https://mizar.uwb.edu.pl/
Would something be a proof in that sense even if it did use Mizar? As far as I can tell, Mizar has no complete reference for its language semantics, except for the single closed-source implementation. In general, information about the system itself (outside of the library) seems very scarce, or at least scarcely advertised.
[1] https://github.com/MizarProject/system [2] https://github.com/digama0/mizar-rs [3] https://arxiv.org/pdf/2304.08391v2 [4] https://link.springer.com/article/10.1007/s10817-018-9479-z