Bashtard is one letter away from bastard. You're stretching if you're reading it as retard.

I initially read it as a play on "bastard". But I'm not so sure it's a stretch. I know more than one person who likes to add the -tard suffix to all sorts of words, used in an offensive way, and it's quite hard to pronounce in a way that doesn't sound like that.

It’s 0 letters away from bash ‘tard, and not really a stretch to speculate that the name might be intentionally a pun that has both meanings.

it's 4 letters away from 'tard' since it requires the removal of letters.

That's like saying "Scunthorpe" is 0 letters away from 'cunt'.

Based on the blurb in the article, I think (though it's not fully clear) that the author intends "bash retard".