Why did that happen?

[mukul]

See the attached image
the face appears to be washed by light. but there was no direct light onto the lens

Why did that happen and what is the technique to overcome it

alternately is it a problem with equipment? [ 600D+18-135 v1]

 

[privatebydesign]

Its flare from the sun in the background.

To minimize it you could move to the left and duck down a little so the rug/material is blocking it, use a lens hood, don't use a 'protective' filter etc.

It is not a fault with your gear per se, your technique will make a much bigger difference.

 

[mrzero]

The front element of your lens, or the filter in front of your lens, may also need cleaning. That could make the flare from the backlighting even worse.

 

[Mt Spokane Photography]

I'd suggest not posing the subject in front of a window, since the sun or even bright light does not light the subject, so when the camera sets exposure for the subjects face, the window is overexposed. If the sun is shining thru the window, it only gets worse, and flare becomes a problem.