Are `UTC_TIMESTAMP ()` and `CONCAT (UTC_DATE (), '', UTC_TIME ())` functionally identical?

**EDIT:**

When I tested it, `UTC_TIMESTAMP()` does not return a UNIX TIMESTAMP. (with MariaDB 10.x)
[![enter image description here](https://i.stack.imgur.com/T4Qtt.png)](https://i.stack.imgur.com/T4Qtt.png)