Marketing_Guy - 3:12 pm on Apr 5, 2012 (gmt 0)
It sounds like he's setup a blog for link building purposes, so removing links from that site to your main site could cause your rankings to drop.
Essentially those links were supporting your rankings to a degree.
It's worth noting that although he's technically correct in his explanation, it would have been easy enough for Google to devalue the blog and remove any benefit your site gets from the links so the effect would have been the same.
Lesson learned here is to shoot for a diverse back link profile and not rely too heavily on one source of links (but given you only dropped a few places, it's not the end of the world).