My data was wiped when trying to boot into recovery and I will tell you exactly what I did:
turned off my Lenovo Tab 10 device
holding "volume up" button and then "power" button at once
released power button after seeing Lenovo logo and hold "volume up" button until I saw Android logo and the text lower:
Wiping data... Format... or something like that. I really want to figure out what I did wrong because I don't want to accidentally lose my data again. And it's very weird that I didn't find any topic which is related with my problem.
P. S. before that I successfully booted into fastboot mode and unlocked bootloader.