Is this an academic discourtesy?
If I understand your question and comments correctly, the sequence of events is this:


The editor handles your paper at time X.
The editor submits their own paper, with a submission timestamp after X.
The editor does not cite you.


If this is the case, then the editor should certainly have been aware of your paper at the time that they submitted their own, and thus been able to cite you.

Failing to cite you thus seems likely to be a case of scientific dishonesty.  There are, however, certain circumstances where failure to cite might be acceptable, such as:


Other papers similar to yours are already cited (e.g., "phenomenon X has been noted a number of times, including [cite, cite, cite]")
You are somehow misinterpreting the date stamps


From what you've written, however, it seems unlikely that one of these cases applies, and more likely that you're dealing with a case of dishonesty.