So they know (or assume?) she received benefits but have made a guess as to which ones, it seems. When info in an article begins "A source said...", a big pinch of salt is required IMO! The red tops do love anything benefit-related, after all.
From the bottom of the article:
"The Department for Work and Pensions refused to give details about any benefits paid to anyone at the house.
A spokeswoman said: As this is a police matter, we are unable to provide a comment. All queries should be directed to Police Scotland.
Police declined to comment on the DWPs involvement."