Flashing stock firmware via SD card will relock an unlocked bootloader. However, it will remove TWRP recovery and reinstall stock recovery. If you need to root again, you must go through the whole bootloader unlock process again (which is no longer officially supported by Huawei).
Check the MD5 checksum if provided. A corrupted UPDATE.APP will cause a "failed" flash mid-way, potentially bricking the device. Huawei Y560-l01 Firmware Sd Card