The customer claims that the application (.NET) when querying for some data returns data different from when the customer looks into the data table directly
Assuming the view does not actually transform the data, technically it is possible if a corruption occurs. View retrieves data from one index, 'table' retrieves from another (ie. from clustered) and the two are out of sync. A DBCC CHECKDB should reveal the problem.
But human error is much more likely, ie. they are looking at different table than the view, or at different records.