It's a sequence of Unicode characters that's supposed to render as the Welsh flag. The first character U+1F3F4 BLACK FLAG seems to be missing (at least when I copy and paste it); that's followed by "tag letters" from the U+E0061-U+E007A spelling "gbwls". See https://unicode.org/reports/tr51/#valid-emoji-tag-sequences
I think the BLACK FLAG is getting removed by HN's emoji filtering, but the modifier characters after it are remaining.
Thanks for the explanation. On my phone, so tools for diagnosis are lacking, but it sounds like you might know your Unicode better than I do anyway. :-)
I think the BLACK FLAG is getting removed by HN's emoji filtering, but the modifier characters after it are remaining.