It would be just he uses a similar email, say last+first@gmail and gives it out incorrectly at times. Or people assume it is his. My friend has a first+last@gmail and I constantly confuse the order (or was it last+first? idk), a decade later. So you two are just seeing a subset of incorrectly addressed email, imo.

I remember a decade+ ago when this was discovered as some issue and caused a bunch of drama in the blogosphere.