Well, the certainly aren't the biggest shareholder of Lowes.
Capital Research & Mgmt (American Funds) is.
Walmart isn't even in the top 20 shareholders. Also, if they were going to buy it, they would do a tender offer, not slowly accumulate shares.
In addition, from those who have dealt with them on the banking side, they are among the most tight lipped company around. If they were going to buy them, it wouldn't be talked about on a fishing trip to the lake.