That could be possible if you advertise snapdeal.com in AdWords and that ads are shown on flipkart.com.. Simple as that.
I have simply highlighted the best answer to your page in Green circle. That says: Which sites did people visit immediately before this site. I may agree with Fer0. This is calculated on the basis of user behavior. You can see that Google.co.in is having the maximum concentration, i.e. a user firstly search for products to buy on Google then visit snapdeal.com. We can see the entry- exit, referring pages or all traffic in analytics too. Now let's think the user after getting results on Google - visited Flipkart & hopefully founds a deal sponsored by snapdeal then - landed on snapdeal.com , here the site visited immediately before snapdeal is flipkart. I am in doubt as Google Ads links are displayed either google paid/ppc, not the site where advertisement was clicked.
Your images says "Which sites did people visit immediately before this site?" - This means, user visit 'flipkart' just after visiting 'snapdeal'. This doesn't mean that snapdeal is getting traffic from the keyword "flipkart". You have misunderstood the alexa status. Here for an example, I explained the user behavior in below image. This is how it works. Hope you get it now.
Hi AppyArry. Is it so? Kindly read your sentence once again... I hope this illustration is not relevant to context. This is something on which Google determines the "Impression Share" and "CTR" related to the keyword "shopping websites online in India".
Keyword was just an example to show you how a user can get into search results and how did they find the website to visit. I'm not saying you are wrong but I have explained it just in a different way. You are right about the impression share and CTR and what I have explained it about the user behavior. Thread opener asked "Goto alexa check snapdeal, i notice that 7% of traffic snapdeal getting from flipkart.com. They each are competitor, HOW IS IT POSSIBLE?" I have concluded to that context only.
AppyArry, the first picture shows that 7.1% of visitors to snapdeal visited flipcart.com just before visit to snapdeal. They exited flipcart and entered snapdeal in one click (that i presume, i don't know how google uses direct input of url in address bar). And I answered AdWords solution for that problem. I cannot remember any other reason for that kind of behavior? Expect maybe user clicking through his bookmarks. Ashutosseo should help us with information which web page is his. Regards.
Google can track one external page to another, via Google Analytics. Both sites have it installed, and therefore the referrer on the 2nd site would of been the 1st site. to the OP: If you drill down in your referrals, you will be able to see exactly where the traffic is coming from (ie. the complete url on your competitors site). As others have mentioned, its probably google content network banners or something.