Hanlon's razor: "Never attribute to malice that which is adequately explained by stupidity." Occam's razor is "the simplest explanation is most likely to be true". Hanlon's razor is a special case of Occam's razor if you assume that stupidity is simpler than malice, which is a hard statement to prove in concrete terms, but intuitively seems to be true.

Stupidity is simpler than malice because a plan that seems dumb would need to be far more complex to be secretly smart and malicious than to just actually be dumb.

Ah yes, the wrong razor. Or, like you say, a more general version of it that might still apply (but wasn't the one I was thinking of).