I, too, had one in my spam folder (although only one, others are coming to inbox normally).
I checked, and the message is: DKIM Signed, SPF Passed, and completely valid headers throughout. That means they spam-foldered it based on content/keywords.
(DKIM = digital signature... usually spammers don't have valid dkim. SPF = similar to DKIM, and again, spammers don't usually bother doing this properly.)