I think I remember a similar post but didn't find it in the seach.
Credit report says "high probability SSN belongs to another". Is this SAR reportable if it reaches the $5000 threshold? If not?

It has "potential SAR" written all over it, but you shouldn't file without doing at least some additional research. Where did you obtain the SSN you submitted to the credit reporting agency? Was it given to you orally from memory, or did you see a Social Security card (does anyone actually carry these any longer)? I'd recommend asking the applicant about the discrepancy and see what shakes out.

Then, if you believe there is ID theft going on, I'd file.