If a variable declaration is made where the right-hand side is a function type with properties, it wraps the result inside a metatable instead of just assigning the value.

Easier to explain with example:
https://typescripttolua.github.io/play#code/JYOwLgpgTgZghgYwgAgGIFcQICoE8AOKA3gFDLnIAUAlAFzIBuA9sACZkX5RP71wi4SAXxIkYmBGGBMQyAOYQwGLHkI16ynAWIdyCGQGcmAGwgA6Y0zmUARArA3qu5PpAGwyGMgC8Vat4A+UgoQl0MTc0trGwQ4Y1NWR2cREJgzLh4fZABmZyhFdChZGGFRV3dGOPQUX3tNVQgaEgB6ZuQuUDADZDtFG2QwAHdgJBIGKsanceNqptbkYG6QYGMSDvBKaer07nwnFra4o2RB7hA5EnKPLYgAJiybkiA