My bank flagged my feedPress purchase as possibly fraudulent

This happens infrequently, but often when banks block or are suspicious of a transaction they'll get in touch with the cardholder.

It's hard to say why it's triggered in any particular instance because generally the banks themselves don't know; their models for predicting fraud generally look at hundreds of different things—and in our experience the answers we've received from banks about why a particular charge was flagged have been varied and contradictory.
Since these kinds of scenarios are seldom, it's not a large concern. Since you know FeedPress is reputable, you can tell your bank it's a non issue.