There are a few different explanations Shrike can think of for this fellow's explanation. The most likely of which being the usual tending to more or less see all fayblood as similar. It's not an entirely uncommon attitude, even if it is a rather exasperating one.

"If you mean to say you know some fayblood child, you should know that that alone is far from suggesting any relation. And simply appearing different does not mean a resemblance."

This may be a bit of a sore point at times.