How do you know they didn't have multiple confirmations from different anonymous sources? Generally this is the case with high quality journalism (souce: dated a journalist).
"Secret Service officials said, speaking on the condition of anonymity"
Their only stated source is "USSS officials" who bafflingly demand "anonymity." I would expect the reporter to tell those /officials/ they need to allow a direct quote or to provide another source; otherwise, their information simply won't be printed.
It's the difference between being a blind mouthpiece and being a reporter.
No well trained journalist would ever write a story like this without verifying the information in redundant ways. If they didn't do that then they probably already know it's fake and could literally write anything they wanted to support the narrative.
A) Well trained journalists and editors are not stupid. B) If they write something false they already know it's false 99% of the time and are doing it for other reasons.
In light of A + B it makes no sense to rely on what is written in the article to support the idea that it is false or undersourced.